The 65-year-old Biden has been a senator since 1972, which could serve as a counterbalance to criticism on the campaign trail that Obama, a first-term senator, lacks experience.
In response to the announcement, Obama's challenger Sen. John McCain, R-Ariz., began running a television ad with footage of Biden saying during one of the early debates that Obama was not prepared to be president and saying he would be honored to run with or against McCain.
Former presidential candidate Sen. Hillary Clinton, D-N.Y., praised the choice, calling Biden "an exceptionally strong, experienced leader and devoted public servant." She said he would be a "purposeful and dynamic vice president."
Recently, the struggling economy has supplanted Iraq as a top campaign issue, but the conflict in Georgia with Russian forces has returned foreign policy to the public discourse. Biden traveled to Georgia in mid-August at the behest of President Mikhail Saakashvili, according to his Web site.
Biden at first supported the use of military force in Iraq but later became an outspoken critic of the war. He has offered a five-point plan on Iraq that includes a limited central government and separate, ethnic regions that have local control over police, education, jobs and services.
On the issue of abortion, he supports a partial-birth abortion ban but not overturning Roe v. Wade.
Biden, a Catholic, was born in Scranton, Pa. on Nov. 20, 1942, the oldest of four children. He grew up in New Castle, Del., graduated from the University of Delaware in 1965 and from the Syracuse University College of Law in 1968.
Before entering the Senate, Biden was an attorney in Wilmington, Del., and served on the New Castle County Council from 1970 to 1972.
In November 1972, Biden was elected to the U.S. Senate. In December of that year, his wife Neilia and their three children were involved in a car accident in which his wife and daughter, Naomi, died. Two other children, Beau and Hunter, survived.
Biden was sworn in as senator in January 1973. Two years later, he became a member of the Senate Foreign Relations Committee, which he currently chairs. He also chaired the Judiciary Committee from 1987 to 1994, and still is a member of that panel.
In 1977, Biden married school teacher Jill Jacobs, and they have a daughter Ashley.
Biden had his own close brush with death in February 1988, when he was hospitalized for suffering two brain aneurysms. It was seven months before he could return to his Senate seat, according to the Associated Press.
Known for his occasional gaffes, Biden's first presidential bid ended in disaster a year before the 1998 election, marred by accusations of plagiarism, including using parts of speeches made by a British Labor Party leader. In 2004, Biden decided against running, saying he doubted he could raise enough funds to challenge opponents.
