Kerry was born in a Denver military hospital, the son of Richard Kerry, a World War II pilot and diplomat, and Rosemary Forbes Kerry, a member of the wealthy Forbes family and a descendant of John Winthrop (Winthrop, John), first governor of Massachusetts Bay Colony. John Kerry, educated in New England and Switzerland, was a successful student and athlete who nurtured a longtime interest in politics. After graduating from Yale University in 1966, he enlisted in the U.S. Navy and served in the Vietnam War as an officer of a gunboat in the Mekong delta. By the time he returned from Vietnam in 1969, he had achieved the rank of lieutenant and had been honoured with a Silver Star, a Bronze Star, and three Purple Hearts.

Concluding his military service in 1970, he questioned the purpose and execution of the war and was a cofounder of the Vietnam Veterans of America and a spokesperson for the Vietnam Veterans Against the War. In this role he gained national attention in 1971 when he testified before the Senate Foreign Relations Committee. The following year he ran unsuccessfully for the U.S. House of Representatives and enlisted in the Naval Reserve. In 1976 he graduated from Boston College Law School and became assistant district attorney in Middlesex county, Massachusetts, winning notice for his tough stance on organized crime. From 1979 he practiced law privately for a few years before resuming his political career. In 1982 he was elected lieutenant governor of Massachusetts, and in 1984 he won election to the U.S. Senate. He was reelected three times (1990, 1996, and 2002).

As senator, Kerry fought for campaign finance reform, investment in public education, and deficit reduction. In his freshman term he began an unofficial investigation that persuaded a bipartisan congressional committee to open hearings on the Iran-Contra Affair. He also pursued scandals in banking and, along with Republican Senator John McCain (McCain, John) of Arizona, was known for helping to normalize relations with Vietnam by clearing up the status of American veterans declared POW/MIA (prisoner of war or missing in action). Kerry chaired several committees, most notably the Foreign Relations Committee (2009– ).

Kerry's first marriage, to Julia Thorne (in 1970), ended in divorce in 1988. In 1995 he married Teresa Heinz, widow of John Heinz (a Republican senator from Pennsylvania) and heiress to the Heinz Company fortune.

After securing the Democratic nomination, Kerry chose as his running mate John Edwards (Edwards, John), a U.S. senator from North Carolina who had contended ably for the primary nomination. Campaigning in the general election against incumbent President George W. Bush (Bush, George W.), Kerry touted plans to reduce joblessness and the national deficit, increase access to health care, and roll back Bush's tax cuts for the wealthiest. Kerry also called for greater diplomacy in foreign affairs and pointed to the administration's failure to capture terrorist Osama bin Laden and to achieve peace in Iraq (see Iraq War). In an election with a huge voter turnout, Kerry suffered a narrow defeat.

Kerry wrote The New War: The Web of Crime That Threatens America's Security (1997) and A Call to Service (2003).