The Los Angeles coastal area was settled by the Tongva (Gabrieleños) and Chumash tribes. Los Angeles would eventually be founded on the village of iyáangẚ or Yaanga (written "Yang-na" by the Spanish), meaning "poison oak place."

Maritime explorer Juan Rodríguez Cabrillo claimed the area of southern California for the Spanish Empire in 1542 while on an official military exploring expedition moving north along the Pacific coast from earlier colonizing bases of New Spain in Central and South America.Gaspar de Portolà and Franciscan missionary Juan Crespí, reached the present site of Los Angeles on August 2, 1769.

In 1771, Franciscan friar Junípero Serra directed the building of the Mission San Gabriel Arcángel, the first mission in the area. On September 4, 1781, a group of forty-four settlers known as "Los Pobladores" founded the pueblo they called El Pueblo de Nuestra Señora la Reina de los Ángeles, 'The Town of Our Lady the Queen of the Angels'. The present-day city has the largest Roman Catholic archdiocese in the United States. Two-thirds of the Mexican or (New Spain) settlers were mestizo or mulatto, a mixture of African, indigenous and European ancestry. The settlement remained a small ranch town for decades, but by 1820, the population had increased to about 650 residents. Today, the pueblo is commemorated in the historic district of Los Angeles Pueblo Plaza and Olvera Street, the oldest part of Los Angeles.

New Spain achieved its independence from the Spanish Empire in 1821, and the pueblo continued as a part of Mexico. During Mexican rule, Governor Pío Pico made Los Angeles Alta California's regional capital.

Mexican rule ended during the Mexican–American War: Americans took control from the Californios after a series of battles, culminating with the signing of the Treaty of Cahuenga on January 13, 1847.

Railroads arrived with the completion of the transcontinental Southern Pacific line from New Orleans to Los Angeles in 1876 and the Santa Fe Railroad in 1885.Petroleum was discovered in the city and surrounding area in 1892, and by 1923, the discoveries had helped California become the country's largest oil producer, accounting for about one-quarter of the world's petroleum output.

By 1900, the population had grown to more than 102,000, putting pressure on the city's water supply. The completion of the Los Angeles Aqueduct in 1913, under the supervision of William Mulholland, ensured the continued growth of the city. Because of clauses in the city's charter that prevented the City of Los Angeles from selling or providing water from the aqueduct to any area outside its borders, many adjacent cities and communities felt compelled to annex themselves into Los Angeles.

Los Angeles created the first municipal zoning ordinance in the United States. On September 14, 1908, the Los Angeles City Council promulgated residential and industrial land use zones. The new ordinance established three residential zones of a single type, where industrial uses were prohibited. The proscriptions included barns, lumber yards, and any industrial land use employing machine-powered equipment. These laws were enforced against industrial properties after-the-fact. These prohibitions were in addition to existing activities that were already regulated as nuisances. These included explosives warehousing, gas works, oil-drilling, slaughterhouses, and tanneries. Los Angeles City Council also designated seven industrial zones within the city. However, between 1908 and 1915, Los Angeles City Council created various exceptions to the broad proscriptions that applied to these three residential zones, and as a consequence, some industrial uses emerged within them. There are two differences from the 1908 Residence District Ordinance and later zoning laws in the United States. First, the 1908 laws did not establish a comprehensive zoning map as the 1916 New York City Zoning Ordinance did. Second, the residential zones did not distinguish types of housing; it treated apartments, hotels, and detached-single-family housing equally.

In 1910, Hollywood merged into Los Angeles, with 10 movie companies already operating in the city at the time. By 1921, more than 80 percent of the world's film industry was concentrated in LA. The money generated by the industry kept the city insulated from much of the economic loss suffered by the rest of the country during the Great Depression. By 1930, the population surpassed one million. In 1932, the city hosted the Summer Olympics.

During World War II, Los Angeles was a major center of wartime manufacturing, such as shipbuilding and aircraft. Calship built hundreds of Liberty Ships and Victory Ships on Terminal Island, and the Los Angeles area was the headquarters of six of the country's major aircraft manufacturers (Douglas Aircraft Company, Hughes Aircraft, Lockheed, North American Aviation, Northrop Corporation, and Vultee). During the war, more aircraft were produced in one year than in all the pre-war years since the Wright brothers flew the first airplane in 1903, combined. Manufacturing in Los Angeles skyrocketed, and as William S. Knudsen, of the National Defense Advisory Commission put it, "We won because we smothered the enemy in an avalanche of production, the like of which he had never seen, nor dreamed possible."

In the 1930s–1940s, Los Angeles county was the national leader in agriculture.

Following the end of World War II, Los Angeles grew more rapidly than ever, sprawling into the San Fernando Valley. The expansion of the Interstate Highway System during the 1950s and 1960s helped propel suburban growth and signaled the demise of the city's electrified rail system, once the world's largest.

Previous to the 1950s, Los Angeles' name had multiple pronunciations, but the soft "G" pronunciation is universal today. Some early movies or video shows it pronounced with a hard "G" ().Sam Yorty was one of the last public figures who still used the hard "G" pronunciation.

Racial tensions led to the Watts riots in 1965, resulting in 34 deaths and over 1,000 injuries.

In 1969, California became the birthplace of the Internet, as the first ARPANET transmission was sent from the University of California, Los Angeles (UCLA) to the Stanford Research Institute in Menlo Park.

In 1973, Tom Bradley was elected as the city's first African American mayor, serving for five terms until retiring in 1993. Other events in the city during the 1970s included the Symbionese Liberation Army's South Central standoff in 1974 and the Hillside Stranglers murder cases in 1977–1978.

In 1984, the city hosted the Summer Olympic Games for the second time. Despite being boycotted by 14 Communist countries, the 1984 Olympics became more financially successful than any previous, and the second Olympics to turn a profit; the other, according to an analysis of contemporary newspaper reports, was the 1932 Summer Olympics, also held in Los Angeles.

Racial tensions erupted on April 29, 1992, with the acquittal by a Simi Valley jury of four Los Angeles Police Department (LAPD) officers captured on videotape beating Rodney King, culminating in large-scale riots.

In 1994, the 6.7 Northridge earthquake shook the city, causing $12.5 billion in damage and 72 deaths. The century ended with the Rampart scandal, one of the most extensive documented cases of police misconduct in American history.

In 2002, Mayor James Hahn led the campaign against secession, resulting in voters defeating efforts by the San Fernando Valley and Hollywood to secede from the city.

Los Angeles will host the 2028 Summer Olympics and Paralympic Games, making Los Angeles the third city to host the Olympics three times.

The 2010 United States Census reported Los Angeles had a population of 3,792,621. The population density was 8,092.3 people per square mile (2,913.0/km²). The age distribution was 874,525 people (23.1%) under 18, 434,478 people (11.5%) from 18 to 24, 1,209,367 people (31.9%) from 25 to 44, 877,555 people (23.1%) from 45 to 64, and 396,696 people (10.5%) who were 65 or older. The median age was 34.1 years. For every 100 females, there were 99.2 males. For every 100 females age 18 and over, there were 97.6 males.

There were 1,413,995 housing units—up from 1,298,350 during 2005–2009—at an average density of 2,812.8 households per square mile (1,086.0/km²), of which 503,863 (38.2%) were owner-occupied, and 814,305 (61.8%) were occupied by renters. The homeowner vacancy rate was 2.1%; the rental vacancy rate was 6.1%. 1,535,444 people (40.5% of the population) lived in owner-occupied housing units and 2,172,576 people (57.3%) lived in rental housing units.

According to the 2010 United States Census, Los Angeles had a median household income of $49,497, with 22.0% of the population living below the federal poverty line.

According to the 2010 Census, the racial makeup of Los Angeles included: 1,888,158 Whites (49.8%), 365,118 African Americans (9.6%), 28,215 Native Americans (0.7%), 426,959 Asians (11.3%), 5,577 Pacific Islanders (0.1%), 902,959 from other races (23.8%), and 175,635 (4.6%) from two or more races.Hispanics or Latinos of any race were 1,838,822 persons (48.5%). Los Angeles is home to people from more than 140 countries speaking 224 different identified languages.Ethnic enclaves like Chinatown, Historic Filipinotown, Koreatown, Little Armenia, Little Ethiopia, Tehrangeles, Little Tokyo, Little Bangladesh, and Thai Town provide examples of the polyglot character of Los Angeles.

Non-Hispanic whites were 28.7% of the population in 2010, compared to 86.3% in 1940. The majority of the Non-Hispanic white population is living in areas along the Pacific coast as well as in neighborhoods near and on the Santa Monica Mountains from the Pacific Palisades to Los Feliz.

Mexican ancestry make up the largest ethnic group of Hispanics at 31.9% of the city's population, followed by those of Salvadoran (6.0%) and Guatemalan (3.6%) heritage. The Hispanic population has a long established Mexican-American and Central American community and is spread well-nigh throughout the entire city of Los Angeles and its metropolitan area. It is most heavily concentrated in regions around Downtown as East Los Angeles, Northeast Los Angeles and Westlake. Furthermore, a vast majority of residents in neighborhoods in eastern South Los Angeles towards Downey are of Hispanic origin.

The largest Asian ethnic groups are Filipinos (3.2%) and Koreans (2.9%), which have their own established ethnic enclaves—Koreatown in the Wilshire Center and Historic Filipinotown. Chinese people, which make up 1.8% of Los Angeles's population, reside mostly outside of Los Angeles city limits and rather in the San Gabriel Valley of eastern Los Angeles County, but make a sizable presence in the city, notably in Chinatown. Chinatown and Thaitown are also home to many Thais and Cambodians, which make up 0.3% and 0.1% of Los Angeles's population, respectively. The Japanese comprise 0.9% of LA's population, and have an established Little Tokyo in the city's downtown, and another significant community of Japanese Americans is in the Sawtelle district of West Los Angeles. Vietnamese make up 0.5% of Los Angeles's population. Indians make up 0.9% of the city's population.

The Los Angeles metropolitan area is home to a large population of Armenians, Assyrians, and Iranians, many of whom live in enclaves like Little Armenia and Tehrangeles.

African Americans have been the predominant ethnic group in South Los Angeles, which has emerged as the largest African American community in the western United States since the 1960s. The neighborhoods of South Los Angeles with highest concentration of African Americans include Crenshaw, Baldwin Hills, Leimert Park, Hyde Park, Gramercy Park, Manchester Square and Watts. Apart from South Los Angeles, neighborhoods in the Central region of Los Angeles, as Mid-City and Mid-Wilshire have a moderate concentration of African Americans as well.

According to a 2014 study by the Pew Research Center, Christianity is the most prevalently practiced religion in Los Angeles (65%). The Roman Catholic Archdiocese of Los Angeles is the largest archdiocese in the country.Cardinal Roger Mahony, as the archbishop, oversaw construction of the Cathedral of Our Lady of the Angels, which opened in September 2002 in Downtown Los Angeles.

In 2011, the once common, but ultimately lapsed, custom of conducting a procession and mass in honor of Nuestra Señora de los Ángeles, in commemoration of the founding of the City of Los Angeles in 1781, was revived by the Queen of Angels Foundation and its founder Mark Albert, with the support of the Archdiocese of Los Angeles as well as several civic leaders. The recently revived custom is a continuation of the original processions and masses that commenced on the first anniversary of the founding of Los Angeles in 1782 and continued for nearly a century thereafter.

With 621,000 Jews in the metropolitan area, the region has the second-largest population of Jews in the United States. Many of Los Angeles's Jews now live on the Westside and in the San Fernando Valley, though Boyle Heights once had a large Jewish population prior to World War II due to restrictive housing covenants. Major Orthodox Jewish neighborhoods include Hancock Park, Pico-Robertson, and Valley Village, while Jewish Israelis are well represented in the Encino and Tarzana neighborhoods, and Persian Jews in Beverly Hills. Many varieties of Judaism are represented in the greater Los Angeles area, including Reform, Conservative, Orthodox, and Reconstructionist. The Breed Street Shul in East Los Angeles, built in 1923, was the largest synagogue west of Chicago in its early decades; it is no longer in daily use as a synagogue and is being converted to a museum and community center. The Kabbalah Centre also has a presence in the city.

The International Church of the Foursquare Gospel was founded in Los Angeles by Aimee Semple McPherson in 1923 and remains headquartered there to this day. For many years, the church convened at Angelus Temple, which, when built, was one of the largest churches in the country.

Los Angeles has had a rich and influential Protestant tradition. The first Protestant service in Los Angeles was a Methodist meeting held in a private home in 1850 and the oldest Protestant church still operating, First Congregational Church, was founded in 1867. In the early 1900s the Bible Institute Of Los Angeles published the founding documents of the Christian Fundamentalist movement and the Azusa Street Revival launched Pentecostalism. The Metropolitan Community Church also had its origins in the Los Angeles area. Important churches in the city include First Presbyterian Church of Hollywood, Bel Air Presbyterian Church, First African Methodist Episcopal Church of Los Angeles, West Angeles Church of God in Christ, Second Baptist Church, Crenshaw Christian Center, McCarty Memorial Christian Church, and First Congregational Church.

The Los Angeles California Temple, the second-largest temple operated by The Church of Jesus Christ of Latter-day Saints, is on Santa Monica Boulevard in the Westwood neighborhood of Los Angeles. Dedicated in 1956, it was the first temple of The Church of Jesus Christ of Latter-day Saints built in California and it was the largest in the world when completed.

The Hollywood region of Los Angeles also has several significant headquarters, churches, and the Celebrity Center of Scientology.^{[citation needed]}

Because of Los Angeles's large multi-ethnic population, a wide variety of faiths are practiced, including Buddhism, Hinduism, Islam, Zoroastrianism, Sikhism, Baháʼí, various Eastern Orthodox churches, Sufism, Shintoism, Taoism, Confucianism, Chinese folk religion and countless others. Immigrants from Asia for example, have formed a number of significant Buddhist congregations making the city home to the greatest variety of Buddhists in the world. The first Buddhist joss house was founded in the city in 1875.Atheism and other secular beliefs are also common, as the city is the largest in the Western U.S. Unchurched Belt.

As home to Hollywood and its entertainment industry, numerous singers, actors, celebrities and other entertainers live in various districts of Los Angeles.