A popular mainstream Democrat with liberal tendencies, the Massachusetts senator's attempt to win his party's endorsement was at first overshadowed by rival Howard Dean's campaign in late 2003 and early 2004.
But Kerry bounced back with some early caucus and primary election victories in the spring of 2004 and easily won the Democrat nomination in July.
A decorated war hero, Kerry supported the attack on Iraq and wants to see a strong US military, but that hawkish stance is balanced by his promotion of healthcare coverage, workers' rights and environment-friendly practices.
Kerry lacks his opponent's charisma and is often criticised for changing his position on various issues. Many dissatisfied Americans will reportedly vote for him not because they are enthusiastic about his policies or style, but because he is not Bush.
John Forbes Kerry was born in 1943 in Denver, Colorado but was raised in several countries because his father was a diplomat abroad.
After graduating from Yale University in 1966, Kerry joined the navy and served in Vietnam with distinction, earning a Silver Star, a Bronze Star, and three Purple Hearts.
Spouse: Teresa Heinz Kerry
Current post: US senator, Massachusetts (1985-present)
Military Record: US Navy (1966-1970). Served in Vietnam. Awarded Silver Star, Bronze Star, and three Purple Hearts
But after he left the navy in 1970, Kerry became known for his opposition to the conflict and in 1971 he helped found and became a spokesman for Vietnam Veterans Against the War.
After a failed attempt for Congress in 1972, Kerry, gained a law degree at Boston College in 1976 and worked as a public prosecutor and then district attorney in Massachusetts.
But Kerry took the political stage in 1982 when he was elected lieutenant governor of Massachusetts. And his second attempt to reach Washington succeeded in 1985 when he entered the US Senate.
Kerry made a name for himself on the Senate Foreign Relations Committee, where he headed the subcommittee on narcotics and terrorism. The body exposed the role of President Ronald Reagan's aide Colonel Oliver North in smuggling guns to the Contra rebels in Nicaragua.
In recent years, the relatively liberal senator has shown an interest in renewable energy, political financing reform, and the threat posed by designated terrorist organisations and drug cartels.
Kerry wants a strong US military
boosted by the latest technology
Kerry has criticised the White House for eroding civil liberties through its domestic security clampdown. He says the Justice Department has stigmatised "innocent Muslims and Arabs who pose no danger".
Besides aiming to put more fuel-efficient cars on US roads, Kerry would repeal some of President George Bush's tax cuts and put the revenue towards expanding health insurance and benefits, as well as promoting student community service programmes.
Kerry backed the Bush's invasion of Iraq to topple Saddam Hussein. But using some unusually colourful language, he has suggested Bush's handling of the war has been "f****ed up".
He says Bush misled Americans on the degree that Iraq posed threat and accuses Bush of not working closely enough with the wider international community. He says excluding France and Germany from rebuilding Iraq was "dumb and insulting".
The senator has expressed concern that the Bush administration is neglecting Afghanistan and issues such as nuclear proliferation and security. He says a strong US military deploying the latest technology is essential.
He supports "free trade", but wants the effects of trade agreements on workers and the environment to be considered more carefully.
Like most of the US political establishment, Kerry is pro-Israeli and sees Palestinian armed resistance to occupation as a key problem. But he also says Israel must curb its settlement policy in accordance with the Bush "road map" plan and has criticised the construction of its controversial West Bank wall.
"He and I bled and almost died on the same battlefield and he's got the qualities we want in a president with our country threatened from terrorists abroad and with the economy."
- Max Cleland, former Georgia senator
"He speaks the language of the Kennedys, which now sounds flowery and phony... Nuggets of nothing, wrapped in pretentious rhetoric, compounded by the pretence of plain speaking."
- Slate magazine
Kerry has come under fire for fudging the Iraq issue: supporting an attack on Iraq without a clear UN endorsement and then criticising Bush for taking a unilateralist approach.