Claire Squires was determined to "change lives" by running the London Marathon and raising money for a mental health charity.
The 30-year-old collapsed and died just over a kilometre from the finish line of the 42 kilometre race, but her legacy will live on thanks to the generosity of those moved by her sudden death.
Ms Squires died on the course near Buckingham Palace on Sunday, local time, London's Daily Telegraph reported.
News of her death touched many across Britain, with tens of thousands of people visiting her JustGiving.com donations profile to give more than $300,000.
Before her death she had raised more than $700.
She had been running to raise money for British group Samaritans, an emotional support service for people in Britain and Ireland, where her mother Cilla had volunteered for 24 years.
On her profile, she wrote: "it was just going to be for fun, but its a fab opportunity to raise money for my charity the samaritans. if everyone i know could donate £5.00 that would be a great help and change lives".
Samaritans chief executive Catherine Johnstone said: "This is an incredibly sad time for Claire's family and all those who knew her.
"We desperately wish that it was not under these circumstances but we have been overwhelmed by the response from people donating in Claire's memory.
"These donations will be put into a tribute fund and, following discussions with the family, will go towards projects they feel would have been important to Claire."
Tests to find out the cause of Ms Squires's death will be done in coming days, the newspaper reported.
The report said Ms Squires, a hairdresser from North Kilworth, Leics, had run the London Marathon in 2010 and had climbed Mount Kilimanjaro in Tanzania - the tallest mountain in Africa - to raise money for the Royal Air Forces Association, which supports war veterans.
Claire is an inspiration to us all. She brought laughter and love to everyone's life
Nicola Short paid tribute to Ms Squires on the RAF Association website.
She said: "Claire is an inspiration to us all. She brought laughter and love to everyone's life. She will be sorely missed by all.
"Our thoughts and prayers are with her family and friends at this time."
Her family, parents Priscilla and Paul and three sisters, were being comforted by friends after her death.
Her 26-year-old brother Grant Squires died in 2002 from a possible overdose just days after his girlfriend had died in a car crash.
Cilla Squires told the inquest into his death that the family had been supporting him through his drug problem and he appeared to be turning his life around when he met his girlfriend.
Ms Squires's death was the 10th in the 31-year history of the London Marathon.