A proud liberal who called Republican President Richard Nixon the most corrupt president in history, McGovern represented his state in Congress for more than 20 years. He was elected to his first of three South Dakota senate terms in 1962.
"George McGovern dedicated his life to serving the country he loved," President Barack Obama said in a statement. "When the people of South Dakota sent him to Washington, this hero of war became a champion for peace ... George was a statesman of great conscience and conviction."
McGovern was a decorated bomber pilot in World War II who became an early critic of the Vietnam War. The South Dakota native once said that he learned to hate war by waging it.
He ran for president three times, winning the Democratic nomination in 1972, but lost out to Mr. Nixon in a landslide. It was a campaign dishonored by Watergate, a scandal that fully unfurled too late to knock Mr. Nixon from his place as a commanding favorite.
In recent years, McGovern turned his focus from politics to world hunger. He served as U.S. ambassador to the Rome-based United Nation's food agencies from 1998 to 2001 and spent his later years working to feed needy children around the world. He and former Republican Sen. Bob Dole collaborated to create an international food for education and child nutrition program, for which they shared the 2008 World Food Prize.
"I want to live long enough to see all of the 300 million school-age kids around the world who are not being fed be given a good nutritional lunch every day," McGovern said in 2006.
McGovern died at the Dougherty Hospice House in Sioux Falls, S.D., at about 5:15 a.m., surrounded by family and friends.
"George believed deeply in public service. It defined him as a Senator and as a man," Vice President Joe Biden said in a statement. "Above all, George McGovern was a generous, kind, honorable man. He will be missed."
The Associated Press contributed to this report.