Gareth Thomas speaking about his HIV status has already started to shift public perceptions of the virus, according to a charity.
The former Wales rugby captain says he hopes to create an "everlasting" legacy of "breaking stigma".
In a new video, released to mark World AIDS Day, he tells the Duke of Sussex: "I always felt like my life was to play rugby and to represent Wales, which I did with all the passion I have.
"But I actually feel that my rugby gave me the platform to do what I do now.
"I believe what I do now is really what I care about because there's not many people from a simple life like I come from who can have the power to change other people's lives."
Prince Harry says what Thomas is doing is "genuinely transformational" and that he's "turned a negative into a positive" to give himself "a new purpose in life".
Speaking about the impact of his work, the rugby star added: "I sit down with my parents sometimes and we look at my trophy cabinet, which I'm really proud of. But I look at it and I think they'll gather dust and they'll go away and they'll be forgotten about.
"But I'd like to think where we're going on this journey of education and breaking stigma around HIV is something that will have a legacy everlasting."
The sportsman first spoke openly about living with the virus in September, and the Terrence Higgins Trust says it's already seeing the impact of what it calls "the Gareth Thomas effect".
Polling carried out by YouGov for the charity has found 74% of the public are aware of Thomas' diagnosis, with 11% saying it improved their overall knowledge of the virus.
But campaigners say there's still a long way to go to overcome the ingrained misconceptions held by some.
The same poll found 39% would feel uncomfortable kissing someone with HIV.
Only 21% correctly knew that someone living with HIV, and on effective treatment, can't pass it on.
Ian Green, chief executive of the Terrence Higgins Trust, told Sky News: "For many people, HIV is stuck back in the 1980s with the tombstone campaign, so for somebody like Gareth - a national treasure - to talk about their HIV status chips away at that stigma, bit by bit."
Mr Green believes many people are not aware of the medical advances which have transformed how HIV is treated. He says it's something very personal to him.
"I'm living with HIV, I'm on effective treatment, I have an undetectable viral load, it is impossible for me to transmit the virus to somebody else," he added.
Alco Tippersma, who is from London and has been living with HIV since 2013, says he hopes Thomas' campaigning will lead to more people getting tested for HIV.
"The way he's handling it now is just brilliant. He's showing you can live a healthy life being HIV positive," he said. "Which is vital."
Mr Tippersma developed AIDS because he was unaware of his HIV status.
"There was a period when I wasn't sure if I'd survive, which I think shows the importance of getting tested early," he added.
Gareth Thomas has joined a new independent HIV Commission, which aims to end new transmissions of the virus in the UK by 2030.