Mr Foot was elected Labour leader in 1980, succeeding Jim Callaghan, but stood down after a heavy defeat in the 1983 election to Margaret Thatcher.
Mr Foot, who was also a prolific writer, was first elected to Parliament in 1945 and was an MP for 42 years.
Prime Minister and Labour leader Gordon Brown led the tributes, describing Mr Foot as a "man of deep principle and passionate idealism". And Lady Thatcher said he was "a great parliamentarian and a man of high principles".
CORRESPONDENT'S VIEW
Mike Sergeant, Political CorrespondentMichael Foot is being remembered by politicians at Westminster with great affection. No doubt, he was one of the finest parliamentarians of his day. A spellbinding orator, the former Labour leader enthralled the Commons and captured audiences far beyond.
He wasn't made for slick sound-bites or 24-hour news. He was never known for sartorial elegance. Michael Foot was a politician from a different age. But, those who knew him best describe a man of integrity and honesty - a deep thinker and an idealist from a time when politicians could be heroes.
Michael Foot made a promise never to take a seat in the Lords - a promise he kept. "Straight as a die" was how one MP described him today. He was a man of conviction whose career spanned a time of enormous change in Britain and the world.
His period as Labour leader coincided with one of the most turbulent periods in the party's history.
Some will credit him with stopping Labour's complete disintegration as the "gang of four" broke away to form the SDP. Others will highlight his role in Labour's disastrous election campaign of 1983.
Ultimate political success would elude Michael Foot. He stood up for what he believed in, even if it made him unpopular. But, across the political spectrum, MPs are today paying warm tribute to one of the greats.
As it happened: Reaction and tributes Obituary: Michael Foot Mr Foot died shortly before 0700 GMT at his home in Hampstead, north London. He had been ill for some time with fading health and had been receiving 24-hour care.
A lifelong peace campaigner and left wing rebel, Mr Foot led the Labour Party during one of the most turbulent periods in its history - with senior figures on the right breaking away to form their own party, the SDP.
He was forced to quit as leader after just three years when Labour suffered its heaviest election defeat in 50 years, with a left wing manifesto dubbed "the longest suicide note in history".
But he is remembered as one of the great Parliamentary orators and debaters, whose intellect and wide interests outside politics - and his sometimes untidy appearance on the campaign trail - belonged to an era before spin and presentation took over politics.
Gordon Brown described him as a "unifying leader" of the Labour Party and a "genuine British radical" who would be remembered with affection by people from across the political spectrum.
Paying tribute to his personal friend outside Downing Street, the prime minister said: "Michael Foot was a man of deep principle and great idealism.
"He was the best Parliamentary debater of his generation and one of the most eloquent, and indeed one of the most humorous, speakers I think the country has ever had."
He said Mr Foot would be mourned as a "man who was good, compassionate and dedicated to his country".
'Remarkable man'Former PM Tony Blair said Mr Foot was "a giant of the Labour movement" who "took over the leadership at the most difficult time in Labour's history and conducted himself with huge dignity".
"I will always remember his personal kindness to me... Even when he disagreed with me, he was immensely supportive and kind."
Announcing Mr Foot's death in the House of Commons, Justice Secretary Jack Straw compared one speech he gave in 1980 to a "Mozart concerto", saying he was "held in very great affection in all sections of the House and the country".
Lord Kinnock, who followed Michael Foot as Labour leader, said his predecessor had held the party together after the SDP breakaway - the "grimmest, darkest hour in its modern history".
"The fact that the party survived as a recognisable political entity at all is attributable to the commitment, conviction, sheer guts and self-sacrifice of Michael Foot," he told the BBC.
"People were devoted to Michael Foot as they are devoted to few politicians."
Lord (Denis) Healey, a former Chancellor of the Exchequer, who Mr Foot defeated in the 1980 leadership contest, said: "I am very sorry indeed. Although I disagreed with him on issues - he was far to the left of me - I was glad to serve as his deputy."
And Tony Benn, who stood against Mr Healey for the deputy leadership in 1981 despite Mr Foot's appeal for him to avoid a divisive battle, also paid tribute.
He told BBC News Mr Foot always "meant what he said" and was "what the Labour Party's all about".
Conservative leader David Cameron described Mr Foot as a "remarkable man", adding: "I'm obviously not old enough to have been in the House of Commons at the same time, but reading some of his speeches (they) were incredibly powerful."
Mr Cameron added: "He was a very intelligent, witty, amusing and thoughtful man."
Liberal Democrat leader Nick Clegg said Mr Foot's "intellectual integrity" was an example to everyone in politics.
"Michael Foot was a great parliamentarian, a great intellectual and a great idealist. He always stood up for what he believed in, even if that meant inviting unpopularity at times."
Nuclear disarmamentMr Foot first stood for Parliament in 1935, but he began his career as a journalist - editing the London Evening Standard by the age of 28. He had two spells as editor of left-wing journal Tribune, a magazine he would continue to contribute to into old age.
HAVE YOUR SAY <blockquote>He was an honest man who found himself in a rapidly changing politically world where image is more important than principle</blockquote>
rational_thinkerSend us your comments He entered Parliament in 1945, in Clement Attlee's post war landslide and became a fierce champion of left wing causes as well as a founder member of the Campaign for Nuclear Disarmament.
He was thrown out of the Parliamentary Labour Party for two years because he opposed increases in defence spending.
Mr Foot first became MP for Plymouth Devonport, before going on to represent for Ebbw Vale and Blaenau Gwent.
Before being elected Labour leader, he was Employment Secretary in the 1974-76 Labour government under Harold Wilson and went on to become Leader of the Commons between 1976 and the 1979 general election.
