Farmer's plan was to send black and white demonstrators to the most segregated areas in the hope that racists would react, thus creating such disorder that the federal government would be forced to intervene to uphold the law. Within a fortnight, on a roadside in Anniston, Alabama, he had his wish, when a mob slashed the tyres of a bus carrying freedom riders and then firebombed it.
Other protesters met brutal violence at the hands of Ku Klux Klansmen and the police - sometimes working together - in Birmingham and Montgomery, which eventually led to a showdown between the civil rights movement and the Kennedy administration.
At one point, as a gang of whites laid siege to the riders, the Rev Martin Luther King and worshippers in a church in Montgomery, the US attorney general, Robert Kennedy, pleaded with King to persuade Farmer to call off the rides so there could be a cooling off period. "Please tell the attorney general that we have been cooling off for the past 350 years," Farmer told King. "If we cool off any more, we'll be in the deep freeze."
The rides went on to Jackson, Mississippi, where hundreds of protesters were arrested, but finally achieved both their immediate goal of integrating inter-state travel and the wider aim of highlighting racial segregation in the south.
It was Farmer's finest hour. For the next few years his name would be up there with the early titans of the civil rights movement - King, Roy Wilkins, of the National Association for the Advancement of Colored Peoples, and Whitney Young, of the National Urban League. But subsequent Core campaigns failed to capture the popular imagination and Farmer saw his position as leader of the radical grassroots taken by Stokely Carmichael and John Lewis, of the Student Nonviolent Co-ordinating Committee.
In 1963, Farmer passed up his best chance to maintain his profile when he refused to bail himself out of jail in Plaquemine, Louisiana, in order to address the march on Washington, where King made his "I have a dream" speech. His decision was a principled one. Since those with whom he had protested could not afford bail, Farmer thought it would be wrong to abandon them.
But it became the greatest regret of his political life. "There was an international audience there and I had a chance to talk to them all. Instead, I had to sit in a jail cell in Louisiana and listen to it on the radio," he said.
So it was not until January 1998, when he went to the White House to receive the presidential medal of freedom, the highest civilian honour, from President Clinton, that Farmer returned to the political centre stage. "When I came into the hotel lobby after the ceremony and everybody cheered it felt just like old times. I finally felt that my work had been recognised."
Farmer always blamed his fall on the fact that he had a white wife - which attracted criticism from blacks and whites in equal measure - and on King's assassination, which, he argued, lead to the slain leader's deification. But equally damaging was his decision to join the Nixon administration as a senior official of the housing, education and welfare department.
"It is my conviction that blacks achieve maximum political leverage by not being 'in the bag' for either party," he said at the time. But his involvement with Republicans, albeit for only a couple years, left many of his former activist-colleagues wary of the strength of his commitment. For a man who spent most of his adult life confronting prejudice with pacifism, this suspicion caused great pain.
Born to a preacher and a former teacher in Texas, Farmer, a teenager of precocious intellect, had intended to be a minister and studied theology at Howard, the black university in Washington. But when his father asked him what he planned to do upon graduation in 1941, he answered: "Destroy segregation."
Soon afterwards he founded Core - which began by challenging the colour bar in a Chicago doughnut shop - and after years working for trade unions and other civil rights groups, he took on running the organisation as a full-time job.
A tall, well-built man with a deep, resonant voice and a sharp sense of humour, Farmer's leadership style was often described as effective and efficient, but criticised for being unnecessarily territorial. Respected for his ability to get things done, he frustrated colleagues who felt his desire for a high media profile for Core, and by extension himself, hindered co-operation with other civil rights groups.
Almost 20 years ago, after the death of his wife Lula, with whom he had two daughters, who survive him, Farmer moved to the rural outpost of Spotsylvania, Virginia, to a house by a lake, where he wrote his memoirs, Lay Bare The Heart. After losing both legs and his sight to diabetes, he remained a visiting professor of history at Mary Washington college in the area.
James Farmer, civil rights activist, born January 12, 1920; died July 9, 1979