US President Barack Obama has led tributes to George McGovern, who vowed to end the Vietnam War but lost an election to Richard Nixon in 1972.
McGovern died about early Sunday at the Dougherty Hospice House in Sioux Falls, South Dakota, surrounded by relatives and friends, his family said in a statement.
The three-term senator, a former World War II bomber pilot, was credited with bringing women, youths and minorities into the Democratic Party in a broad-based White House campaign that foundered after revelations of his running mate's battle with mental illness.
'We are blessed to know that our father lived a long, successful and productive life advocating for the hungry, being a progressive voice for millions and fighting for peace,' the family statement read.
President Barack Obama praised McGovern as a man who 'dedicated his life to serving the country he loved' and as 'a statesman of great conscience and conviction'.
Vice-President Joe Biden said he was 'honoured' to serve with McGovern in the US Senate 'and to call him a friend'.
And, in a joint statement, former president Bill Clinton and his wife Hillary, currently serving as secretary of state, said McGovern 'always worked to advance the common good and help others realise their potential.
'Of all his passions,' the Clintons said, 'he was most committed to feeding the hungry, at home and around the world.'
McGovern's legacy even drew praise from Republican former House speaker Newt Gingrich, who said he had 'a very good sense of humour' and was 'just a great guy'.
McGovern's 1972 campaign, which harnessed growing opposition to the Vietnam War, was built on a grassroots movement that expanded the Democratic Party from its base among the urban white workers and unions to women, minorities and student activists - the core of today's party.
Both Bill and Hillary Clinton entered politics while working for the campaign when they were in their mid-20s, and many McGovern supporters returned the favour during Hillary's primary battle with Barack Obama in 2008.
The campaign however suffered a fatal blow when McGovern's running mate, Missouri Senator Thomas Eagleton, was forced to quit the ticket after it emerged that he had been hospitalised on three occasions and given electroshock therapy.
McGovern had not known about Eagleton's history of depression, which in part explains why candidates now typically conduct exhaustive background checks on prospective running mates.
McGovern lost to Nixon in one of the most dramatic landslides in US history, winning only Massachusetts and the District of Columbia. The term 'McGovern liberal' became a favourite taunt of Republicans for decades.
Nixon went on to end direct US military involvement in Vietnam with the signing of the Paris Peace Accords in January 1973. However, Nixon was forced to resign two years later in the infamous Watergate scandal, named for the burglary of McGovern's party headquarters less than five months before his election defeat.
McGovern lamented his 1972 defeat in a Washington Post op-ed last month, saying: 'I wanted to win for our party, our young soldiers, and the men and women of goodwill disaffected by Watergate and turned off by the power of big money in politics.'
But 'at the wise old age of 90, I can say that losing the presidency was one chapter in a long, complex and richly happy life in which I learned that you can't always control all the outcomes'.