On December 1, 1955 in Montgomery, Alabama, Parks, age 42, refused to obey bus driver James Blake's order that she give up her seat to make room for a white passenger. Her action was not the first of its kind. Irene Morgan in 1946, and Sarah Louise Keys in 1955, had won rulings before the U.S. Supreme Court, and the Interstate Commerce Commission, respectively, in the area of interstate bus travel. Nine months before Parks refused to give up her seat, 15-year-old Claudette Colvin refused to move from her seat on the same bus system. But unlike these previous individual actions of civil disobedience, Parks' action sparked the Montgomery Bus Boycott.

Parks' act of defiance became an important symbol of the modern Civil Rights Movement and Parks became an international icon of resistance to racial segregation. She organized and collaborated with civil rights leaders, including boycott leader Martin Luther King, Jr., helping to launch him to national prominence in the civil rights movement.

At the time of her action, Parks was secretary of the Montgomery chapter of the National Association for the Advancement of Colored People (NAACP) and had recently attended the Highlander Folk School, a Tennessee center for workers' rights and racial equality. Nonetheless, she took her action as a private citizen "tired of giving in". Although widely honored in later years for her action, she suffered for it, losing her job as a seamstress in a local department store. Eventually, she moved to Detroit, Michigan, where she found similar work. From 1965 to 1988 she served as secretary and receptionist to African-American U.S. Representative John Conyers. After retirement from this position, she wrote an autobiography and lived a largely private life in Detroit. In her final years she suffered from dementia and became embroiled in a lawsuit filed on her behalf against American hip-hop duo OutKast.

Parks eventually received many honors ranging from the 1979 Spingarn Medal to the Presidential Medal of Freedom, the Congressional Gold Medal and a posthumous statue in the United States Capitol's National Statuary Hall. Her death in 2005 was a major story in the United States' leading newspapers. She was granted the posthumous honor of lying in state at the Capitol Rotunda.

Rosa Parks was born as Rosa Louise McCauley in Tuskegee, Alabama on February 4, 1913, to James McCauley and Leona Edwards, respectively, a carpenter and a teacher, and was of African-American, Cherokee-Creek, and Scots-Irish ancestry. Parks' great grandfather was a Scottish-Irishman. She was small, even for a child, and she suffered poor health and had chronic tonsillitis. When her parents separated, she moved with her mother to Pine Level, just outside Montgomery, Alabama. There she grew up on a farm with her maternal grandparents, mother, and younger brother Sylvester, and began her lifelong membership in the African Methodist Episcopal Church. She attended rural schools until the age of eleven, then enrolled at the Industrial School for Girls in Montgomery where she took academic and vocational courses. Parks then went on to a laboratory school set up by the Alabama State Teachers College for Negroes for secondary education but was forced to drop out to care for her grandmother, and later for her mother, after they became ill.

Under Jim Crow laws, black and white people were segregated in virtually every aspect of daily life in the South, including public transportation. Bus and train companies did not provide separate vehicles for the different races but did enforce seating policies that allocated separate sections for blacks and whites. School bus transportation was unavailable in any form for black schoolchildren in the South. Parks recalled going to elementary school in Pine Level, where school buses took white students to their new school and black students had to walk to theirs: "I'd see the bus pass every day... But to me, that was a way of life; we had no choice but to accept what was the custom. The bus was among the first ways I realized there was a black world and a white world."

Although Parks' autobiography recounts that some of her earliest memories are of the kindness of white strangers, her situation made it impossible to ignore racism. When the Ku Klux Klan marched down the street in front of her house, Parks recalls her grandfather guarding the front door with a shotgun. The Montgomery Industrial School, founded and staffed by white northerners for black children, was burned twice by arsonists, and its faculty was ostracized by the white community.

In 1932, Rosa married Raymond Parks, a barber from Montgomery, at her mother's house. Raymond was a member of the NAACP, at the time collecting money to support the Scottsboro Boys, a group of black men falsely accused of raping two white women. After her marriage, Rosa took numerous jobs, ranging from domestic worker to hospital aide. At her husband's urging, she finished her high school studies in 1933, at a time when less than 7% of African Americans had a high school diploma. Despite the Jim Crow laws that made political participation by black people difficult, she succeeded in registering to vote on her third try.

In December 1943, Parks became active in the Civil Rights Movement, joined the Montgomery chapter of the NAACP, and was elected volunteer secretary to its president, Edgar Nixon. Of her position, she later said, "I was the only woman there, and they needed a secretary, and I was too timid to say no." She continued as secretary until 1957. In the 1940s, Parks and her husband were members of the Voters' League. Sometime soon after 1944, she held a brief job at Maxwell Air Force Base, a federally owned area where racial segregation was not allowed, and rode on an integrated trolley. Speaking to her biographer, Parks noted, "You might just say Maxwell opened my eyes up." Parks worked as a housekeeper and seamstress for a white couple, Clifford and Virginia Durr. The politically liberal Durrs became her friends and encouraged Parks to attend—and eventually helped sponsor her—at the Highlander Folk School, an education center for workers' rights and racial equality in Monteagle, Tennessee, in the summer of 1955.

Many people were moved by the brutal murder of Emmett Till in August 1955. On November 27, 1955—only four days before she refused to give up her seat—she later recalled that she had attended a mass meeting in Montgomery which focused on this case as well as the recent murders of George W. Lee and Lamar Smith. The featured speaker at the meeting was T.R.M. Howard, a black civil rights leader from Mississippi who headed the Regional Council of Negro Leadership.