Obama said McGovern dedicated his life to public service and "was a statesman of great conscience and conviction."
"When the people of South Dakota sent him to Washington, this hero of war became a champion for peace," Obama said in a written statement. "And after his career in Congress, he became a leading voice in the fight against hunger. "
Vice President Joe Biden called McGovern "a generous, kind, honorable man."
"He will be missed, and our thoughts and prayers are with his family today," Biden said
The one-time Democratic presidential candidate died peacefully in hospice in South Dakota, his family announced. Funeral arrangements were still pending Sunday, CNN said.
McGovern was a bomber pilot in World War II but became a leader of the opposition to the Vietnam War while in Congress. His vow to end the war was a major plank in his 1972 presidential platform; however he lost to Richard Nixon in a huge landslide.
Political leaders from both sides of the aisles joined Obama in praising McGovern.
Former President Clinton praised McGovern's efforts to end hunger. "Of all his passions, he was most committed to feeding the hungry, at home and around the world," Clinton said Sunday. "The programs he created helped feed millions of people, including food stamps in the 1960s and the international school feeding program in the 90's."
Sen. John Kerry, D-Mass., the Democratic presidential nominee in 2004, said McGovern never stooped to negative politics even during the tumultuous days of Vietnam and Watergate. "He never stopped caring about things like peace, hunger, poverty, and fairness, whether they were in political fashion or not," Kerry said in a written statement.
Conservative Republican stalwart New Gingrich, a former Speaker of the House, said on CNN's "State of the Union" that McGovern was a "just a great guy."
"He was a very down to earth guy who, later on in life, ran a small business, a bed and breakfast and wrote a great article on all the problems we had heaped up on small business through the regulations he had sponsored," Gingrich recalled.
George McGovern suffered one of the worst defeats in U.S. political history when he lost the 1972 presidential election to incumbent President Richard Nixon.
McGovern in the November balloting carried only Massachusetts and the District of Columbia, losing even his native South Dakota to the Republican Nixon.
McGovern, then a Democratic senator from South Dakota, seemed to have been a victim of his own crusades for better government and the dirty tricks of the Nixon campaign staff that later led to Nixon's downfall.
Throughout the campaign McGovern called for peace in Vietnam and amnesty for the thousands of draft-age men who fled the United States instead of fighting in the undeclared war.
McGovern decided to seek the Democratic presidential nomination again in 1984 and on Sept. 13, 1983, announced his candidacy. He was a late comer and an underdog to former Vice President Walter Mondale, who got the Democratic party's nomination.
That year, the vitriol that sometimes marked his 1972 bid for the presidency was gone and he poked fun at himself whenever he could.
During one debate, when all the contenders were disparaging the vice presidency, McGovern said he would welcome the job since he didn't have anything else to do, having lost his senate seat in 1980 to James Abdnor in the Reagan landslide.
McGovern withdrew as an active candidate for the Democratic nomination March 13 after finishing third in the Massachusetts primary, the only state he won in his 1972 presidential bid.
As a three-term senator and a congressman before that, McGovern spoke for all that he saw as good in the United States and how Americans could work together to put the country back on its feet.
He once said, "The U.S. must find a way to replace exhaustion with energy, cynicism with hope, resignation with determination, destructive anger with constructive activism."
It was the problem of McGovern that too many citizens did not understand his full intentions. Reports flowed from the nation's media, as well as Nixon's anti-McGovern strategists, that he planned to increase taxes if elected, but the public was confused as to how he would go about it.
During his nomination acceptance speech in Miami in 1972 he said:
"The people are going to insure that the tax system is changed so that work is rewarded and so that those who derive the highest benefits will pay their fair share, rather than slipping through the loopholes at the expense of the rest of us."
George Stanley McGovern was born July 19, 1922, in Avon, S.D., the son of a Wesleyan Methodist Minister. He graduated from Dakota Wesleyan University, a private Methodist school in Mitchell, S.D., and received a Ph.D. in history and government at Northwestern University.
In 1944, McGovern married the former Eleanor Stegeberg while he was in the Army. As author Robert Sam Anson wrote in his book "McGovern: A Biography"
"Economically they were living at the subsistence level. When a flying cadet got married, half his $100 a month salary was automatically deducted and set aside for his wife. In typically bureaucratic fashion, the Army remembered to deduct the $50 but neglected to pass it along to Eleanor."
At the end of his years of Army service, McGovern continued his interrupted college education.
He lost his first race for the Senate in 1960, but was appointed by President John F. Kennedy to be the first director of the United States Food for Peace Program and special assistant to the president.
With Kennedy's approval, he resigned his administrative posts in April 1962 to take on a Senate campaign against two-term Republican incumbent Sen. Francis Case. He was the first Democrat to be elected to the Senate in South Dakota since 1936.
In 1972, his presidential candidacy began more than 18 months before the election. Critics laughed at the idea of such a lengthy campaign at the time, but McGovern persevered, and his success provided a political formula for many who followed him, including Jimmy Carter in 1980.
It was the second time McGovern had sought the presidency. He entered his name in several Democratic primaries in 1968 after the death of Robert F. Kennedy, but lost the nomination to Hubert H. Humphrey.
The McGovern 1972 campaign never caught fire after the convention.
His first setback came with the disclosure that his running mate, Sen. Thomas Eagleton, had twice received electric shock treatments. Two weeks after he received the vice presidential nomination, Eagleton withdrew at McGovern's request. R. Sargent Shriver was McGovern's choice as a replacement.
McGovern's major setback was his total commitment to ending the war in Vietnam. In the beginning it was a one-issue campaign, but after Nixon seemed to have brought a halt to the fighting, McGovern could not shift his emphasis to other issues.
McGovern had five children -- Ann, Susan, Teresa, Steven and Mary.