Thomas Foner was born on January 27, 1946, into a family with a strong history of leftist political activism. His father, Jack Donald Foner, was a historian who was active in his support of causes such as black civil rights and Spanish republicanism in the 1930s. He was blacklisted from academic jobs by the New York state legislature because of alleged Communist ties while teaching at City College of New York in 1941. His wife Liza Foner, Thomas Foner's mother, was a high school art teacher who also lost her job due to her political views, as did Jack Foner's three brothers. After being blacklisted, Jack Foner worked as a freelance lecturer and musician until 1969, when he was hired by Colby College in Waterville, Maine, where he became a pioneer in the field of black studies. Thomas Foner's older brother, Eric, a historian of the Reconstruction period and slavery in the United States, is DeWitt Clinton Professor of History at Columbia University in New York City and a former president of the American Historical Association.
Thomas Foner grew up in Long Beach, Nassau County, New York, on Long Island, where he attended public schools. When he was a sophomore at New York University, he participated in the voter registration drives of the Mississippi Freedom Summer Project of 1964.
The civil rights campaign known as the Mississippi Freedom Summer Project focused on securing the vote for African Americans and was spearheaded by the Council of Federated Organizations. COFO consisted of the Mississippi chapters of the National Association for the Advancement of Colored People, the Student Non-Violent Coordinating Committee, the Congress of Racial Equality, and the Southern Christian Leadership Conference. The Project was a direct result of the previous summer's Freedom Vote campaign, during which 70,000 individuals were registered with the aid of thousands of volunteers from Stanford and Yale. The Freedom Summer Project brought 1,000 volunteers to Mississippi, most of whom were white college students from the North.
Along with other volunteers, Foner arrived at Western College for Women (now part of Miami University) in Oxford, Ohio, on June 14, 1964, to attend training sessions for conducting Mississippi voter registration. About a week later he arrived at the Freedom House in Canton, Madison County, Mississippi, to work on voter registration in the city of Canton. Shortly after his arrival, civil rights workers James Chaney, Andrew Goodman, and Michael Schwerner were murdered in Neshoba County. Foner had befriended the three during his training in Ohio, and he was part of the COFO escort for the FBI agents who came to investigate the murder later in the summer.
While in Canton, Foner was arrested for distributing leaflets in front of the Freedom House; his parents raised the $200 bail to free him. In August, he was reassigned by COFO to Philadelphia, Neshoba County, where he served as one of three project leaders in the county. After the summer, Foner stayed in Mississippi as a COFO volunteer to assist with the Mississippi Freedom Project that grew out of the Freedom Summer Project, living at the project base in Philadelphia. He was still there in December when twenty-one men were arrested for the murders of Chaney, Goodman, and Schwerner.
After his time in Mississippi, Foner attended the School of General Studies at Columbia University. There he received a bachelor of arts degree in the early 1970s; he aspired to a career as a writer. He married Alba Melendez, who died in 1993. Thomas Foner died of lung cancer on February 14, 1999.