Jowell, who was diagnosed with a brain tumor a year ago, used her position in the House of Lords to campaign for better access to experimental treatment and delivered a memorable speech that moved her fellow peers to tears.
The former social worker lost to her Conservative rival, and was defeated again in the following year's general election.
In her speech, she urged colleagues to support the Eliminate Cancer Initiative to improve cancer survival under the NHS, which is the worst in Western Europe. In the process, he said, "she gave hope and opportunity to hundreds of thousands of children".
Sarah Lindsell, CEO of the Brain Tumour Charity, said the charity had started working with "wonderful ambassador" Dame Tessa towards the end of a year ago, and she praised her campaigning for cancer patients.
"My sympathies to her loving family - Dame Tessa's campaigning on brain cancer research is a lasting tribute to a lifetime of public service".
"Despite going through all of that and wanting to spend precious time with her family. she gave up so much of that time to continue to campaign, to ask for change, because it really matters", she told the BBC.
A spokesman for her family said: "It is with great sadness, and an enormous sense of loss, that we announce the death of Tessa Jowell".
She was determined to fight campaigns right to the end of her life and fought the one on cancer bravely, hopefully for the benefit of many other people. "Her strength in raising awareness of her illness and fighting for better treatment for others inspired us all".
Where are Great Britain's London 2012 gold medallists now?
He told the Press Association: "She was universally popular and respected among politicians of all parties".
Coe, who is now President of the International Association of Athletics Federations, said London 2012 would not have happened without Dame Tessa.
"Before the 1997 Labour victory, we worked on a programme to nurture children from the moment of their birth, but crucially also to work with parents and the wider community to transform the lives of those otherwise caught in intergenerational disadvantage".
Sky News broadcaster Kay Burley shared a picture of her with Dame Tessa on Twitter with the caption: "RIP Tessa Jowell".
"Her determination and sense of humour surrounding them was infectious", he tweeted.
"She was the most wise of counsellors, the most loyal and supportive of colleagues, and the best of friends".
Here she took on the job of convincing unsure colleagues about the merits of hosting the Olympics in 2012. And because everything she said or did was intertwined with the personal, she was more effective. "Spent a memorable evening with her at JW3 when she came to speak to a packed audience, who all loved her regardless of their political persuasion". But she was no softie.