Lara Casalotti shared her good news in a video, above, saying: "I'm very excited to tell you some great news, a well-matching donor has been found.
"If all goes to plan I will go to transplant soon. It's amazing to think this person is the one in 25 million."
She continues: "Thanks to everyone's efforts, there are lots of donor drives still planned - I urge everyone to go to these drives and sign up.
"There are still plenty of people who are waiting to find their donor."
In January, people desperately tried to find a stem cell donor to help Lara using the hashtag #Match4Lara, after she developed acute myeloid leukaemia at Christmas whilst visiting Thailand.
As Lara is Thai-Italian, she faced a “needle in a haystack” search as only three per cent of stem cell donors are mixed race.
The flood of new test subjects has also improved the chances for others awaiting matching cells.
Lara’s mother Supanya said: “As a mum, I feel pure relief as we knew that the odds were stacked against Lara. Whoever the donor is, they will never, ever know how grateful I am. The transplant is still a few weeks away and I wish I could wrap them in cotton wool to keep them safe!
“We know we have a long road ahead as a transplant is an extremely serious procedure, but knowing there is a good match for Lara is a weight off our shoulders that we desperately needed.”
The #Match4Lara appeal has been backed by thousands of friends, strangers and celebrities including J.K. Rowling, David Cameron, Gareth Bale, Stephen Fry and Mark Wahlberg.
What is a stem cell transplant?
If a patient has a condition that affects their bone marrow or blood, a stem cell transplant is their best chance of survival. Doctors will give new, healthy stem cells to the patient via their bloodstream, where they begin to grow and create healthy red blood cells, white blood cells and platelets.
In the UK, the Anthony Nolan Trust saw an ‘unprecedented spike’ of new donors from black, Asian, ethnic minority or mixed race backgrounds.
At the campaign’s peak, more than 50 percent of those signing up to the register were from BAME backgrounds, the highest proportion ever seen by the charity.
Lara, who is studying for a Masters in global migration at UCL, will now proceed to the next stage of the transplant process.
Ann O’Leary, Head of Register Development at Anthony Nolan, said: “We’re over the moon that we’ve been able to find a suitable donor for Lara and that she’s now able to begin her transplant journey.
“The life-changing impact of the Match4Lara campaign will be seen for years to come, as any one of the thousands of people they have signed up could save the life of someone like Lara in the future.”