George McGovern, who argued fervently against the Vietnam war as a senator from South Dakota, died before dawn today. He was 90.
"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," his family said in a statement.
A decorated World War II bomber pilot, Senator McGovern said he learned to hate war by waging it.
In his failed presidential contest against Richard Nixon in 1972, he sought to end the conflict in Vietnam and cut military spending by billions of dollars.
He helped to create the Food for Peace programme and spent much of his career believing the United States should be more accommodating with the Soviet Union.
In his first year in office as senator, Mr McGovern took to the Senate floor to say that the Vietnam war was a trap that would haunt the United States - a prescient speech that drew little notice.
As the war escalated, so did his opposition. Late in 1969, he called for a ceasefire in Vietnam and the withdrawal of all US troops within a year.
He later co-sponsored a Senate amendment to cut off appropriations for the war by the end of 1971.
It failed, but not before he had taken the floor to declare: "This chamber reeks of blood" and to demand an end to "this damnable war."
His opposition to armed conflict remained a constant long after he retired.