The original inhabitants of Pasadena (a Chippewa word meaning "Crown of the Valley") and surrounding areas were members of the Native American Hahamog-na tribe, a branch of the Tongva Nation. They spoke the Tongva language (part of the Uto-Aztecan languages group). Native Americans had lived in the Los Angeles Basin for thousands of years.Tongva dwellings lined the Arroyo Seco (Los Angeles County) in present day Pasadena and south to where it joins the Los Angeles River and along other natural waterways in the city.

The native people lived in thatched, dome-shape lodges and lived on a diet of acorn meal, seeds and herbs, venison, and other small animals as well as trading for ocean fish with the coastal Tongva. They made cooking vessels from steatite soapstone from Catalina Island. The oldest transportation route still in existence in Pasadena is the old Tongva foot trail, also known as the Gabrielino Trail, that follows the west side of the Rose Bowl and the Arroyo Seco past the Jet Propulsion Laboratory into the San Gabriel Mountains. The trail has been in continuous use for thousands of years. An arm of the trail is also still in use in what is now known as Salvia Canyon.

The Spanish first colonized the Los Angeles Basin in the 1770s as part of the Viceroyalty of New Spain and built the San Gabriel Mission and renamed the local Tongva people "Gabrielino Indians," after the name of the mission. Today, several bands of Tongva people live in the Los Angeles area.

In 1821, Mexico became independent of Spain and California came under control of the Mexican government. In 1833, the mission lands were secularized and most of the lands in California were granted to private Mexican citizens in the form of ranchos. Present-day Pasadena was divided between Rancho San Rafael (lands west of the Arroyo Seco extending to present-day Burbank in the northwest to Glassell Park in the southwest), Rancho del Rincon de San Pascual, (present-day central Pasadena, Altadena, and South Pasadena), and Rancho Santa Anita (present-day east Pasadena, Arcadia, and Monrovia). Rancho del Rincon de San Pascual was so named because it was deeded on Easter Sunday to Eulalia Perez de Guillén Mariné of Mission San Gabriel Arcángel.

Before the annexation of California in 1848 by the United States at the end of the Mexican-American war, the last of the Mexican owners of Rancho del Rincon de San Pascual was Manuel Garfias who retained title to the property after statehood in 1850. Garfias sold sections of the property to the first Anglo settlers to come into the area: Dr. Benjamin Eaton, the father of Fred Eaton; and Dr. S. Griffin. Much of the property was purchased by Benjamin Wilson, who established his Lake Vineyard property in the vicinity. Wilson, known as Don Benito to the local Indians, also owned the Rancho Jurupa (Riverside, California) and was mayor of Los Angeles. He was the grandfather of WWII General George S. Patton, Jr. and the namesake of Mount Wilson.

In 1873, Wilson was visited by Dr. Daniel M. Berry of Indiana who was looking for a place in the country that could offer a mild climate for his patients, most of whom suffered from respiratory ailments. Berry was an asthmatic and claimed that he had his best three night's sleep at Rancho San Pascual.^{[citation needed]} To keep the find a secret, Berry code-named the area "Muscat" after the grape that Wilson grew. To raise funds to bring the company of people to San Pascual, Berry formed the Southern California Orange and Citrus Growers Association and sold stock in it.^{[citation needed]} The newcomers were able to purchase a large portion of the property along the Arroyo Seco and on January 31, 1874, they incorporated the Indiana Colony. As a gesture of good will, Wilson added 2,000 acres (8 km²) of then-useless highland property, part of which would become Altadena. Colonel Jabez Banbury opened the first school on South Orange Grove Avenue. Banbury had twin daughters, named Jennie and Jessie. The two became the first students to attend Pasadena’s first school on Orange Grove.

At the time, the Indiana Colony was a narrow strip of land between the Arroyo Seco and Fair Oaks Avenue. On the other side of the street was Wilson's Lake Vineyard development. After more than a decade of parallel development on both sides, the two settlements merged into the City of Pasadena.

The popularity of the region drew people from across the country, and Pasadena eventually became a stop on the Atchison, Topeka and Santa Fe Railway, which led to an explosion in growth. From the real estate boom of the 1880s until the Great Depression, as great tourist hotels were developed in the city, Pasadena became a winter resort for wealthy Easterners, spurring the development of new neighborhoods and business districts, and increased road and transit connections with Los Angeles, culminating with the opening of the Arroyo Seco Parkway, California's first freeway. By 1940, Pasadena had become the eighth-largest city in California and was widely considered a twin city to Los Angeles.

The first of the great hotels to be established in Pasadena was the Raymond (1886) atop Bacon Hill, renamed Raymond Hill after construction. Pasadena was served by the Atchison, Topeka and Santa Fe Railway at the Santa Fe Depot in downtown when the Second District was opened in 1887. The original Mansard Victorian 200-room facility burned down on Easter morning of 1895, was rebuilt in 1903, and razed during the Great Depression to make way for residential development. The Maryland Hotel existed from the early 1900s and was demolished in 1934.^{[citation needed]} The world-famous Mount Lowe Railway and associated mountain hotels shut down four years later due to fire damage. Three hotel structures have survived, the Green Hotel (a co-op since 1926), the Vista Del Arroyo (now used as a Federal courthouse), and a residential tower of the Maryland at 80 North Euclid Avenue (a co-op since 1953).

The American Craftsman era in art and design is well represented in Pasadena. The architectural firm Greene and Greene developed the style; many of its residences still stand. Two examples of their Ultimate bungalow are the masterpiece Gamble House, of which public tours are available, and the Robert R. Blacker House, both designated California Historical Landmarks and enrolled on the U.S. National Register of Historic Places.

The Second World War proved to be a boon to Pasadena as Southern California became a major staging area for the Pacific War. High tech manufacturing and scientific companies made the city their home, a trend which continued in the decades following the war, notably with NASA's Jet Propulsion Laboratory, Tetra Tech and Ameron International.

In the 1950s, Pasadena saw a steady influx of people from the Southern United States, especially African-Americans from Texas and Louisiana. Pasadena also began hosting a large immigrant community, particularly from China, Japan, Philippines, esp. Mexico, Guatemala, El Salvador, Italy and Armenia, as well South Asia like India.

The American Academy of Dramatic Arts, founded in 1884 in New York, opened its Pasadena campus in 1974. However, in 2001 the conservatory moved from Pasadena to Hollywood. Training actors for the stage in a two year program, the conservatory was the first school in the United States to offer professional education in the field of acting. Point Loma Nazarene University was located in Pasadena for many years before relocating to San Diego County, and retained the names Pasadena University and Pasadena College.

In 1969, the Pasadena Unified School District was desegregated, though the issue would continue to be fought in court for a decade. A year later, the 210 Freeway was built along a newly chosen route. The freeway's construction was controversial, as it caused the demolition of over a thousand homes, many historic, and many claimed that the route was designed to cut off the city's less wealthy neighborhoods.

Downtown Pasadena became dangerous in some parts and deserted in others, and incidences of murder and arson skyrocketed. Old Pasadena faced destruction as plans for new high-rise developments were drawn up, though they were mostly stopped by increasingly active preservation advocates. Pasadena suffered demographically as many residents decamped for the nearby suburbs or the Inland Empire, causing an overall decrease in population.^{[citation needed]} Despite these setbacks, many local artists and hipsters moved in to take advantage of low property values. Their legacy can be seen today in the Doo Dah Parade which began in 1976.

In 2014, several arrests were made involving an embezzlement scheme which stole money from the UUP. The amount is estimated to be $6.4 million.

The 2010 United States Census reported that Pasadena had a population of 137,122. The population density was 5,928.8 people per square mile (2,289.1/km²). The racial makeup of Pasadena was 76,550 (55.8%) White, 14,650 (10.7%) African American, down from 19.0% in 1990, 827 (0.6%) Native American, 19,595 (14.3%) Asian, 134 (0.1%) Pacific Islander, 18,675 (13.6%) from other races, and 6,691 (4.9%) from two or more races. Hispanic or Latino of any race numbered 46,174 persons (33.7%). Non-Hispanic whites were 38.8% of the population, down from 70.4% in 1970.

The Census reported that 133,629 people (97.5% of the population) lived in households, 2,472 (1.8%) lived in non-institutionalized group quarters, and 1,021 (0.7%) were institutionalized.

There were 55,270 households, out of which 14,459 (26.2%) had children under the age of 18 living in them, 22,285 (40.3%) were married couples living together, 6,131 (11.1%) had a female householder with no husband present, 2,460 (4.5%) had a male householder with no wife present. There were 3,016 (5.5%) unmarried partnerships. 18,838 households (34.1%) were made up of individuals, and 5,748 (10.4%) had someone living alone who was 65 years of age or older. The average household size was 2.42. There were 30,876 families (55.9% of all households); the average family size was 3.18.

The age distribution of the population was as follows: 26,507 people (19.3%) were under the age of 18, 12,609 people (9.2%) aged 18 to 24, 45,371 people (33.1%) aged 25 to 44, 34,073 people (24.8%) aged 45 to 64, and 18,562 people (13.5%) who were 65 years of age or older. The median age was 37.2 years. For every 100 females, there were 95.1 males. For every 100 females age 18 and over, there were 93.5 males.

There were 59,551 housing units at an average density of 2,574.8 per square mile (994.1/km²), of which 24,863 (45.0%) were owner-occupied, and 30,407 (55.0%) were occupied by renters. The homeowner vacancy rate was 2.3%; the rental vacancy rate was 6.6%. 64,306 people (46.9% of the population) lived in owner-occupied housing units and 69,323 people (50.6%) lived in rental housing units^{[citation needed]}.

According to the 2010 United States Census, Pasadena had a median household income of $69,302, with 13.2% of the population living below the federal poverty line.

During 2015–2019, Pasadena had a median household income of $83,068, with 14.5% of the population living below the federal poverty line. For people ages 25 and over, 88.3% had a high school degree or higher while 52.3% had a Bachelor's degree or higher.