Conservative leader David Cameron said he was "incredibly sad" to hear news of her death.
"She was an extraordinary MP, a real battler. Someone who was never prepared to just take the establishment view," said Mr Cameron.
Lib Dem leader Nick Clegg said Mrs Dunwoody was "a fiercely principled and incredibly effective Parliamentarian" who would be "missed on all sides of the House".
Ms Dunwoody's son David described her as a wonderful mother and grandmother.
He told the BBC she had died "in a gentle and calm way" on Thursday evening after being ill for about a week.
He said: "She was a woman who stood up and said what she believed was true. She defended people who didn't have anyone else to defend them.
"Everybody who knew her knew she believed passionately in everything that she did."
Transport Secretary Ruth Kelly, who crossed swords with Ms Dunwoody in appearances before her committee, said the veteran MP would be "sadly missed by her Labour colleagues".
"I always enjoyed my encounters with Gwyneth, but I always made sure I was fully briefed," she added.
Former Commons speaker and Labour MP Baroness Boothroyd, who was a close friend, said she was "a fighter in every respect who just wouldn't give up".
"She was always a rebel, but she was a rebel with a cause," she told BBC Radio 4's The World at One.
Former Labour MP Tony Benn said he was shocked by the news.
He said: "She was an independent-minded woman who always spoke her mind and will be badly missed.
"She was listened to with great attention from the House itself."
Gordon Brown tribute
Ms Dunwoody joined the Labour Party in 1946 and first entered Parliament as the MP for Exeter in 1966. She came from a politically active family: both her grandmothers were suffragettes and her father Morgan Phillips was General Secretary of the Labour Party.
Her mother was a minister in the House of Lords and later became Lord Lieutenant of London.
From 1967 she was a minister on the former Board of Trade, before losing her seat in 1970.
She was elected MP for Crewe in 1974 - which became Crewe and Nantwich in a 1983 boundary change.
She was also a member of the European Parliament from 1974 to 1979.
Thorn in side
Always an independent figure, Mrs Dunwoody was frequently a thorn in the Government's side.
In 2001 she survived an attempt by Labour whips to remove her from the transport select committee - which under her chairmanship often produced highly critical reports.
Backbench Labour MPs refused to support the move when it went to a vote in the Commons.
The Labour MP, Stephen Pound, told the BBC: "The House rose as one to save our Gwyneth."
He said she was an "extraordinary person" and her views always deserved attention.
She was also widely admired by transport industry leaders, many of whom were grilled by her over the years at committee hearings.
George Muir, director-general of the Association of Train Operating Companies, said: "Gwyneth was a passionate supporter of the railway in the UK over many years and never afraid to express strong views on its development.
"We will miss her energy, enthusiasm and good humour. The railway industry has lost a good friend".
Your comments on Gwyneth Dunwoody
I am greatly saddened to hear of the loss of such a formidable and honest person from the House of Commons. She regularly sliced and diced the weasel words of ministers of both major parties and told it the way the rest of us actually knew it was. She is irreplaceable and politics in Britain will be greatly diminished by her passing.
Neil Woodfine, Oxford UK
A sad loss to British politics and a major loss to HM Coastguard who she defended rigorously and justly in our time of need.
John, Northern Ireland
I had the privilege and pleasure to work closely with Mrs. Dunwoody on a number of occasions. She, along with a small number of other MPs, restored my faith in Parliamentary Democracy. She spoke her mind, she spoke for her constituents and she did what she knew instinctively to be right.
Dave Lovell, Paris France
Another blow for the downtrodden. Gwyneth was a breath of sweet fresh air during a time when the very word 'politician' has come to embody mistrust & deceit.
I wrote to her once in connection with transport problems in Wales and she went to a lot of trouble to answer my questions. Her daughter was then Transport Minister in Wales and I also had a letter from her. She was absolutely the cream of parliamentarians and politicians. It's no cliche to say she will be sadly missed.
John Olsson, Welshpool, UK
As a long-standing Conservative I mourn the death of Gwyneth Dunwoody. Tough-minded, outspoken & above all she was thoroughly honest. Alas, not many like her.
Angela Thomas, France
Gwyneth Dunwoody came to talk to us when I was in the 6th form at Malbank School, Nantwich, in her constituency in 1983. We had a General Election that year. Gwyneth was passionate about how the young should vote and shouldn't waste what others had fought so hard for. I had just turned 18 a couple of months before and this was to be my first opportunity to vote, she was an inspirational.
Julie Nield, Melbourne, Australia
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.