The pair ended up losing in a lopsided vote for incumbent Richard Nixon, with the McGovern ticket earning only 17 electoral votes -- from Massachusetts and the District of Columbia -- to Nixon's 520.
McGovern reflected on that defeat in a September piece in The Washington Post, calling it "a significant personal setback" that left him "genuinely stunned."
"The loss is there, an old wound never fully healed. My disappointment was certainly personal, made deeper by the awareness that many thousands of young Americans, and far more Vietnamese and other Asian citizens, were going to and did lose their lives with the Nixon administration's continuation of the war," he wrote. "And I was upset that my supporters would carry the burden of the loss, too -- something that has weighed on me all these years."
But he added, "I am optimistic about the country, and I am convinced that McGovern for President 1972 helped put those ideals within sight and completion today."
Sen. John Kerry said Sunday that McGovern never let the political popularity of a subject determine whether he supported a cause.
"George McGovern was a voice of clarity and conviction at a time when America needed it most," Kerry said. "He spoke to many of us who opposed the war but loved our country, because he was the genuine article, a soft-spoken, decent and gentle man who lived a remarkable life with humility."
After his presidential loss, McGovern returned to the Senate, where he was re-elected in 1974. But he was beaten when he sought a fourth term in 1980, a victim of what became known as the Reagan Revolution that swept conservatives into power and their views into vogue.
Four years later, he tried again to win the Democratic presidential nomination, but dropped out. Former Vice President Walter Mondale became the nominee -- only to lose to Reagan in another lopsided race.
Former Speaker of the House Newt Gingrich said Sunday that McGovern was more than a very down-to-earth man.
"George was actually a very complicated person," Gingrich said. "He was not a pacifist. His argument over Vietnam was about that particular war. He was a citizen."
After leaving the Senate, McGovern taught at a number of schools, including Columbia University, Northwestern University, Cornell University, American University and the University of Berlin. He served as the president of the Middle East Policy Council from 1991 to 1998. President Clinton appointed him ambassador to the United Nations Food and Agriculture Organization in Rome and, in 2000, awarded him the Presidential Medal of Freedom.
In 2001, McGovern was named the first United Nations global ambassador on hunger.
In the 2008 presidential campaign, McGovern switched his allegiance from Hillary Clinton to Barack Obama. But in a 2009 commentary in the Post, he lashed out at the Obama administration over its policies in Afghanistan and reflected on one of the hallmarks of his political life.
"As a U.S. senator during the 1960s, I agonized over the badly mistaken war in Vietnam," McGovern wrote. "After doing all I could to save our troops and the Vietnamese people from a senseless conflict, I finally took my case to the public in my presidential campaign in 1972. Speaking across the nation, I told audiences that the only upside of the tragedy in Vietnam was that its enormous cost in lives and dollars would keep any future administration from going down that road again.
"I was wrong."
In lieu of flowers, the family is requesting donations to Feeding South Dakota.