Evidence of human habitation of the area begins at least 13,000 years ago. Evidence for a Paleoindian presence includes a fluted Clovis-like point found in the 1980s along the western Santa Barbara County coast, as well as the remains of Arlington Springs Man, found on Santa Rosa Island in the 1960s. At least 25,000 Chumash natives lived in the region prior to Spanish contact. Five Chumash villages flourished in the area. The present-day area of Santa Barbara City College was the village of Mispu; the site of the Los Baños pool (along west beach) was the village of Syukhtun, chief Yanonalit's large village located between Bath and Chapala streets; Amolomol was at the mouth of Mission Creek; and Swetete, above the bird refuge.

Spanish explorer Juan Rodríguez Cabrillo, sailing for the Kingdom of Spain, sailed through what is now called the Santa Barbara Channel in 1542, anchoring briefly in the area. In 1602, Spanish maritime explorer Sebastián Vizcaíno gave the name "Santa Barbara" to the channel and also to one of the Channel Islands.

A land expedition led by Gaspar de Portolà visited around 1769, and Franciscan missionary Juan Crespi, who accompanied the expedition, named a large native town "Laguna de la Concepcion". Cabrillo's earlier name, however, is the one that has survived.

The first permanent European residents were Spanish missionaries and soldiers under Felipe de Neve, who arrived in 1782 and constructed the Presidio. They were sent to both secure the Spanish claim to the region and to convert the indigenous peoples to Catholicism. Many of the Spaniards brought their families with them, and those formed the nucleus of the small town – at first just a cluster of adobes – that surrounded the Presidio of Santa Barbara. The Santa Barbara Mission was established on the Feast of Saint Barbara, December 4, 1786. It was the tenth of the California Missions to be founded by the Spanish Franciscans. It was dedicated by Padre Fermín Lasuén, who succeeded Padre Junipero Serra as the second president and founder of the California Franciscan Mission Chain. The Chumash laborers built a connection between the canyon creek and the Santa Barbara Mission water system through the use of a dam and an aqueduct. During the following decades, many of the natives died of diseases such as smallpox, against which they had no natural immunity.

The most dramatic event of the Spanish period was the powerful 1812 earthquake, and tsunami, with an estimated magnitude of 7.1, which destroyed the Mission as well as the rest of the town; water reached as high as present-day Anapamu street, and carried a ship half a mile up Refugio Canyon. The Mission was rebuilt by 1820 after the earthquake. Following the earthquake, the Mission fathers chose to rebuild in a grander manner, and it is this construction that survives to the present day, the best-preserved of the California Missions, and still functioning as an active church by the Franciscans. After the Mexican government secularized the missions in the 1830s, the baptismal, marriage, and burial records of other missions were transferred to Santa Barbara, and now found in the Santa Barbara Mission Archive-Library.

The Spanish period ended in 1822 with the conclusion of the Mexican War of Independence, which terminated 300 years of Spanish colonial rule and transferred control to the newly independent Mexican government.

Santa Barbara street names reflect the influence of the Spanish period. The names de le Guerra and Carrillo come from the Guerra family of California and Carrillo family of California. They were instrumental in building up the town, so they were honored by having streets named after them.

After the forced secularization of the Missions in 1833, successive Mexican Governors distributed the large land tracts formerly held by the Franciscan Order to various families in order to reward service or build alliances. These land grants to local notable families mark the beginning of the "Rancho Period" in California and Santa Barbara history. Fernando Tico was one of the first settlers who received land grants for the local area. Fernando led the Native Americans against the Argentinian pirates in the 1800s. The population remained sparse, with enormous cattle operations run by wealthy families. It was during this period that Richard Henry Dana, Jr. first visited Santa Barbara and wrote about the culture and people of Santa Barbara in his book Two Years Before the Mast.

Santa Barbara fell bloodlessly to a battalion of American soldiers under John C. Frémont on December 27, 1846, during the Mexican–American War, and after the Treaty of Guadalupe Hidalgo in 1848 it became part of the expanding United States.

Change came quickly after Santa Barbara's acquisition by the United States. The population doubled between 1850 and 1860. In 1851, land surveyor Salisbury Haley designed the street grid, famously botching the block measurements, misaligning the streets, thereby creating doglegs at certain intersections. Wood construction replaced adobe as American settlers moved in; during the Gold Rush years and following, the town became a haven for bandits and gamblers, and a dangerous and lawless place. Charismatic gambler and highwayman Jack Powers had virtual control of the town in the early 1850s, until driven out by a posse organized in San Luis Obispo. English gradually supplanted Spanish as the language of daily life, becoming the language of official record in 1870. The first newspaper, the Santa Barbara Gazette, was founded in 1855.

While the Civil War had little effect on Santa Barbara, the disastrous drought of 1863 ended the Rancho Period, as most of the cattle died and ranchos were broken up and sold. Mortimer Cook, a wealthy entrepreneur, arrived in 1871 and opened the city's first bank. Cook later served two terms as mayor. Cook founded the first National Gold Bank of Santa Barbara in 1873. The building of Stearns Wharf in 1872 enhanced Santa Barbara's commercial and tourist accessibility; previously goods and visitors had to transfer from steamboats to smaller craft to row ashore. During the 1870s, writer Charles Nordhoff promoted the town as a health resort and destination for well-to-do travelers from other parts of the U.S.; many of them came, and many stayed. The luxurious Arlington Hotel dated from this period. In 1887 the railroad finally went through to Los Angeles, and in 1901 to San Francisco: Santa Barbara was now easily accessible by land and by sea, and subsequent development was brisk. Santa Barbara had a system of street railways that operated from 1875 through 1929. Begun as a single mule-drawn line from the waterfront pier to the Arlington Hotel, over the decades it was incrementally expanded, later electrified, and operated until its closure in June 1929.

Peter J. Barber, an architect, designed many Late Victorian style residences, and served twice as mayor, in 1880 and again in 1890. A year after Barber's term as mayor, President Benjamin Harrison became the first of five presidents to visit Santa Barbara.

Just before the turn of the 20th century, oil was discovered at the Summerland Oil Field, and the region along the beach east of Santa Barbara sprouted numerous oil derricks and piers for drilling offshore. This was the first offshore oil development in the world; oil drilling offshore would become a contentious practice in the Santa Barbara area, which continues to the present day.

Santa Barbara housed the world's largest movie studio during the era of silent film. Flying A Studios, a division of the American Film Manufacturing Company, operated on two city blocks centered at State and Mission between 1910 and 1922, with the industry shutting down locally and moving to Hollywood once it outgrew the area, needing the resources of a larger city. Flying A and the other smaller local studios produced approximately 1,200 films during their tenure in Santa Barbara, of which approximately 100 survive.

During this period, the Loughead Aircraft Company was established on lower State Street, and regularly tested seaplanes off of East Beach. This was the genesis of what would later become Lockheed.

The magnitude 6.3earthquake of June 29, 1925, the first destructive earthquake in California since the 1906 San Francisco quake, destroyed much of downtown Santa Barbara and killed 13 people. The earthquake caused infrastructure to collapse including the Sheffield Dam. The low death toll is attributed to the early hour (6:44 a.m., before most people were out on the streets, vulnerable to falling masonry). While this quake, like the one in 1812, was centered in the Santa Barbara Channel, it caused no tsunami. It came at an opportune time for rebuilding, since a movement for architectural reform and unification around a Spanish Colonial style was already underway. Under the leadership of Pearl Chase, many of the city's famous buildings rose as part of the rebuilding process, including the Santa Barbara County Courthouse, sometimes praised as the "most beautiful public building in the United States." There is also the unfortunate incident that happened in 1907, which included a horrific train accident that took the lives of 32 people.

During World War II, Santa Barbara was home to Marine Corps Air Station Santa Barbara, and Naval Reserve Center Santa Barbara at the harbor. Up the coast, west of the city, was the Army's Camp Cooke (the present-day Vandenberg Air Force Base). In the city, Hoff General Hospital treated servicemen wounded in the Pacific Theatre. On February 23, 1942, not long after the outbreak of war in the Pacific, the Japanese submarine I-17 surfaced offshore and lobbed 16 shells at the Ellwood Oil Field, about 10 miles (16 km) west of Santa Barbara, in the first shelling attack by an enemy power on the continental U.S. since the bombardment of Orleans in World War I. Although the shelling was inaccurate and only caused about $500 damage to a catwalk, panic was immediate. Many Santa Barbara residents fled, and land values plummeted to historic lows.

After the war many of the servicemen who had seen Santa Barbara returned to stay. The population surged by 10,000 people between the end of the war and 1950. This burst of growth had dramatic consequences for the local economy and infrastructure. Highway 101 was built through town during this period, and newly built Lake Cachuma began supplying water via a tunnel dug through the mountains between 1950 and 1956.

Local relations with the oil industry gradually soured through the period. Production at Summerland had ended, Elwood was winding down, and to find new fields oil companies carried out seismic exploration of the Channel using explosives, a controversial practice that local fishermen claimed harmed their catch. The culminating disaster, and one of the formative events in the modern environmental movement, was the blowout at Union Oil's Platform A on the Dos Cuadras Field, about eight miles (13 km) southeast of Santa Barbara in the Santa Barbara Channel, on January 28, 1969. Approximately 100,000 barrels (16,000 m³) of oil surged out of a huge undersea break, fouling hundreds of square miles of ocean and all the coastline from Ventura to Goleta, as well north facing beaches on the Channel Islands. Two legislative consequences of the spill in the next year were the passages of the California Environmental Quality Act (CEQA) and the National Environmental Policy Act (NEPA); locally, outraged citizens formed GOO (Get Oil Out). Santa Barbara's business community strove to attract development until the surge in the anti-growth movement in the 1970s. Many "clean" industries, especially aerospace firms such as Raytheon and Delco Electronics, moved to town in the 1950s and 1960s, bringing employees from other parts of the U.S. UCSB itself became a major employer. In 1975, the city passed an ordinance restricting growth to a maximum of 85,000 residents, through zoning. Growth in the adjacent Goleta Valley could be shut down by denying water meters to developers seeking permits. As a result of these changes, growth slowed down, but prices rose sharply.

When voters approved connection to State water supplies in 1991, parts of the city, especially outlying areas, resumed growth, but more slowly than during the boom period of the 1950s and 1960s. While the slower growth preserved the quality of life for most residents and prevented the urban sprawl notorious in the Los Angeles basin, housing in the Santa Barbara area was in short supply, and prices soared: in 2006, only six percent of residents could afford a median-value house. As a result, many people who work in Santa Barbara commute from adjacent, more affordable areas, such as Santa Maria, Lompoc, and Ventura. The resultant traffic on incoming arteries, in particular the stretch of Highway 101 between Ventura and Santa Barbara, is another problem being addressed by long-range planners.

Since the middle of the twentieth century, several destructive fires have affected Santa Barbara: the 1964 Coyote Fire, which burned 67,000 acres (270 km²) of backcountry along with 106 homes; the smaller, but quickly moving, Sycamore Fire in 1977, which burned 200 homes; the disastrous 1990 Painted Cave Fire, which incinerated over 500 homes in only several hours, during an intense Sundowner wind event; the November 2008 Tea Fire, which destroyed 210 homes in the foothills of Santa Barbara and Montecito; and the 2009 Jesusita Fire that burned 8,733 acres (35.34 km²) and destroyed 160 homes above the San Roque region of Santa Barbara.

The Thomas Fire burned from its origins in Santa Paula 60 miles (97 km) to the east of Santa Barbara and consumed 281,893 acres (1,140.78 km²) in Santa Barbara and Ventura counties, most of which consisted of rural land and wilderness areas. The fire started December 4, 2017, and was 100% contained by January 12, 2018. 1,050 structures were lost in the Thomas Fire, mostly east of Santa Barbara in Ventura County. The Thomas Fire has been the largest Santa Barbara County fire ever recorded to date.

The 2010 United States Census reported that Santa Barbara had a population of 88,410. The population density was 2,106.6 people per square mile (813.4/km²). The racial makeup of Santa Barbara was 66,411 (75.1%) White; 1,420 (1.6%) African American; 892 (1.0%) Native American; 3,062 (3.5%); Asian (1.0% Chinese, 0.6% Filipino, 0.5% Japanese, 0.4% Korean, 0.4% Indian, 0.2% Vietnamese, 0.4% other); 116 (0.1%) Pacific Islander; 13,032 (14.7%) from other races; 3,477 (3.9%) from two or more races. Hispanics or Latinos of any race were 33,591 persons (38.0%). Non-Hispanic Whites were 45,852 persons (52.2%)

The Census reported that 86,783 people (98.2% of the population) lived in households, 1,172 (1.3%) lived in non-institutionalized group quarters, and 455 (0.5%) were institutionalized.

Of the 35,449 households, 8,768 (24.7%) had children under the age of 18 living in them, 13,240 (37.3%) were opposite-sex married couples living together, 3,454 (9.7%) had a female householder with no husband present, and 1,539 (4.3%) had a male householder with no wife present. There were 2,420 (6.8%) unmarried opposite-sex partnerships, and 339 (1.0%) same-sex married couples or partnerships; 11,937 households (33.7%) were made up of individuals, and 4,340 (12.2%) had someone living alone who was 65 years of age or older. The average household size was 2.45. There were 18,233 families (51.4% of all households); the average family size was 3.13.

The population was spread out, with 16,468 people (18.6%) under the age of 18, 10,823 people (12.2%) aged 18 to 24, 26,241 people (29.7%) aged 25 to 44, 22,305 people (25.2%) aged 45 to 64, and 12,573 people (14.2%) who were 65 years of age or older. The median age was 36.8 years. For every 100 females, there were 98.5 males. For every 100 females age 18 and over, there were 97.7 males.

There were 37,820 housing units at an average density of 901.2 per square mile (347.9/km²), of which 13,784 (38.9%) were owner-occupied, and 21,665 (61.1%) were occupied by renters. The homeowner vacancy rate was 1.3%; the rental vacancy rate was 4.1%; 34,056 people (38.5% of the population) lived in owner-occupied housing units and 52,727 people (59.6%) lived in rental housing units.

As of the census of 2000, 92,325 people*, 35,605 households, and 18,941 families resided in the city. The population density was 4,865.3 people per square mile (1,878.1/km²). There were 37,076 housing units at an average density of 1,953.8 per square mile (754.2/km²). The racial makeup of the city was 74.0% White, 1.8% African American, 1.1% Native American, 2.8% Asian, 0.1% Pacific Islander, 16.4% from other races, and 3.9% from two or more races. People of Hispanic or Latino background, of any race, were 35.0% of the population.

Of the 35,605 households, 24.3% had children under the age of 18 living with them, 39.8% were married couples living together, 9.5% had a female householder with no husband present, and 46.8% were not families. About 32.9% of all households were made up of individuals, and 11.4% had someone living alone who was 65 years of age or older. The average household size was 2.47 and the average family size was 3.17.

In the city, the population was distributed as 19.8% under the age of 18, 13.8% from 18 to 24, 32.3% from 25 to 44, 20.4% from 45 to 64, and 13.8% who were 65 years of age or older. The median age was 35 years. For every 100 females, there were 97.0 males. For every 100 females age 18 and over, there were 95.0 males.

The median income for a household in the city was $47,498, and for a family was $57,880. Males had a median income of $37,116 versus $31,911 for females. The per capita income for the city was $26,466. About 7.7% of families and 13.4% of the population were below the poverty line, including 16.8% of those under age 18 and 7.4% of those age 65 or over. If one compares the per capita income to the actual cost of living, the number of people living below the poverty line is considerably higher.