Thomas Emmett "Tom" Hayden (born December 11, 1939) is an American social and political activist and politician, most famous for his involvement in the anti-war and civil rights movements of the 1960s. He is the father of American actor Troy Garity.

Hayden was born in Detroit, Michigan, to parents of Irish descent, and later attended the University of Michigan, where he was editor of the Michigan Daily and one of the founders of the student activist group Students for a Democratic Society.

In 1961, he married Casey Hayden, a Texas-born civil rights activist who worked for the Student Non-Violent Coordinating Committee. He served as president of SDS from 1962 to 1963, and drafted its most famous work, the Port Huron Statement. From 1964 to 1968, he lived in Newark, New Jersey, where he worked with impoverished inner-city residents as part of the Newark Community Union Project. He was also witness to the city's race riots, and wrote the book Rebellion in Newark: Official Violence and Ghetto Response (1967). Hayden also played a key role in the protests and violence surrounding the 1968 Democratic National Convention in Chicago, Illinois. There, he was arrested as part of the "Chicago Seven," with other protesters including Abbie Hoffman and Jerry Rubin, and charged with conspiracy and inciting riots. He made several high profile trips as a peace activist to Cambodia and North Vietnam during America's involvement in the Vietnam War, including an especially controversial one in 1972 to North Vietnam with his future wife, actress Jane Fonda.

In 1976, Hayden made a maverick primary election challenge against sitting California U.S. Senator John V. Tunney. Starting from far behind, Hayden mounted a spirited challenge and finished a surprisingly close second in the Democratic primary field. He and Fonda went on to found the Campaign for Economic Democracy (CED), which formed a close alliance with then Governor Jerry Brown and successfully promoted solar energy, environmental protection, and renters rights policies while electing some 100 members to local office throughout California.

Hayden later served in the California State Assembly (1982-1992) and the State Senate (1992-2000). Hayden mounted another maverick bid in the Democratic primary for Governor of California in 1994 on the theme of campaign finance reform. He unsuccessfully ran as the Democratic candidate for Mayor of Los Angeles in 1997, defeated by Richard Riordan. In 1999 he made a speech during the 1999 Seattle WTO protests. In 2001 Hayden unsuccessfully sought election to the Los Angeles City Council. He currently lives in Los Angeles, California and is married to actress Barbara Williams. Over the last three years, Hayden has periodically taught as an assistant and adjunct professor at Occidental College, during the fall semesters of 2005 and 2006 he taught a course on Social Movements at Pitzer College.