Sarah Lindsell, chief executive of the Brain Tumour Charity, said: "Tessa Jowell's courage and honesty in speaking about her brain tumour diagnosis, coupled with her fierce determination to improve the lives of others affected by the disease, has already brought hope to an often-forgotten community of patient and families".
She convinced many unsure colleagues about the merits of bidding for the 2012 Olympics.
Councillor Georgia Gould, leader of Camden Council, said her optimism and courage were a "massive inspiration" to many.
The couple parted after it was said to be damaging Dame Tessa's career, but they were later reconciled.
The All-Party Parliamentary Group Against Antisemitism (APPG) said: "Thoughts with the family & friends of Rt Hon Baroness Jowell DBE".
He praised the campaigning she did for more NHS cancer treatments.
Conservative MP for Chatham and Aylesford, Tracey Crouch, said she was very sad to hear the news, adding: "She was respected across the political divide for her calm, polite manner".
Angry and frustration as Edmund's run comes to an end — Madrid Open
But Thiem succeeded in doing the almost impossible with his deep drives: Make Nadal look sluggish and a step slow on clay. I lost the No. 1 before, but what makes me happy is I feel fit, can compete with possibilities every single week.
Tony Blair, under whom Dame Tessa served, said: "Tessa had passion, determination and simple human decency in greater measure than any person I have ever known".
David Cameron shared a picture of himself and Dame Tessa recreating the Beatles' Abbey Road cover, writing: "Devastated that Tessa Jowell has passed away after her incredibly courageous fight". She understood they would be great for the United Kingdom, persuading a sceptical Tony Blair and others that it would be winnable, and helped build key alliances with local authorities, the sports establishment and media. I am not surprised that Tessa Jowell's death has done so, trending as it is on social media with comments and condolences from dozens of national and local politicians, journalists and media commentators, and people from the world of sport and public service. Her last appearance was during votes on the EU Withdrawal Bill - terribly frail but beaming with delight and enthusiasm as we went through the division lobbies.
"But above all she wanted to see Labour in government, and when we were she took her unique style and deep personal commitment into the heart of Whitehall".
He said her impact on politics was enormous and "everything she touched turned to gold in some way, whether it was advancing equal pay for women, starting Sure Start - which is an vast programme for children in our country - or of course bringing the Olympics to Britain".
London Olympics chairman Sebastian Coe said: "Quite simply, without Tessa there would have been no London 2012, and without Tessa they would not have been the success they were".
"But if they were misleading, uncaring or obfuscating she would be tougher than anyone - and forensic with it".
Alastair Campbell, Tony Blair's former Downing Street press secretary paid tribute on Twitter, saying: "RIP Tessa, wonderful woman, superb politician, the kindest friend". She showed unflinching tenacity in persuading the Prime Minister and the Cabinet that the Government should throw its full weight behind the bid. "I will miss her enormously".
Many figures in the sporting world also paid tribute, with Olympic rower Matthew Pinsent tweeting: "RIP Tessa Jowell - absolutely central to the effort to win and stage the Olympics and Paralympics in 2012".