The boycott was precipitated by Rosa Parks' refusal to give up her bus seat in favor of a white passenger. In Montgomery, the dividing line between the front seats reserved for white passengers and the back ones reserved for black passengers was not fixed. When the front of the bus was full, the driver could order black passengers sitting towards the front of the bus to surrender their seat. Rosa Parks' seat was in that border area. When she was arrested on December 1, 1955, the local civil rights organizations, with which Ms. Parks was involved, saw this as the ideal opportunity for political action.
In church meetings with the new minister in the city, Martin Luther King, Jr, a city-wide boycott of public transit as a protest for a fixed dividing line for the segegrated sections of the buses was proposed and passed.
The boycott proved extremely effective, with enough riders lost to the city transit system to cause serious economic distress. Instead of riding buses, boycotters organized a system of carpools, with volunteer car owners carrying people to various destinations. Some white housewives also drove their black domestic servants to work, although it is unclear to what extent this was based on sympathy with the boycott, versus the simple desire to have their staff present and working. When the city pressured local insurance companies to stop insuring cars used in the carpools, the boycott leaders arranged policies with Lloyd's of London.
In response, opposing whites formed chapters of the White Citizens Councils. Like the Ku Klux Klan, the Councils sometimes resorted to violence: Martin Luther King's house was firebombed and boycotters were physically attacked.
The city finally resorted to arresting Dr. King for organizing the boycott. That move backfired by bringing national attention to the protest. Eventually, the United States Supreme Court affirmed a lower court decision that Alabama's racial segregation laws for buses were unconstitutional, handing the protesters a clear victory. This victory led to a city ordinance that allowed black bus passengers to sit virtually anywhere they wanted.
The boycott resulted in the US civil rights movement receiving one of its first victories, and gave Martin Luther King the national attention that would make him one of the prime leaders of the cause.