Dr Alex George is set to advise the government in his new role as a young mental health ambassador.
Downing Street said the A&E doctor would use his clinical expertise and personal experience to help shape policy on improving support for young people in schools, colleges and universities.
The Love Island star launched a campaign to change mental health education after his brother Llŷr took his own life aged 19 last year.
Following a meeting with Boris Johnson, he said he'll be "working closely" with the government to make mental health an "absolute priority".
Sharing the news to his Instagram, Dr Alex posted a picture of himself and the prime minister mid-discussion inside 10 Downing Street.
He captioned the post: "WE DID IT!! You called and the PM answered!! I have been appointed as the Ambassador for Mental Health. It hasn’t sunk in yet and I’m not sure it ever will. I am truly humbled.
"In my role, I will be working closely with the Government to make mental health an absolute priority. Never has mental health been more important than now. From schools to universities, the NHS and the wider public, MENTAL HEALTH MATTERS. For the current as well as future generations, we must do everything in our power to bring meaningful change."
He continued in his post: "Nothing will bring my brother back but if I can make a positive impact that saves even one life, it will be worth moving mountains for."
Meanwhile, Johnson said: “Children and young people have heroically adapted to save lives and protect our NHS.
“This has understandably had a huge impact on their mental health, so I want to shine a spotlight on this vital issue ahead of their return to school.
“I’m delighted that Dr Alex George will be working with us as we do everything in our power to improve people’s mental wellbeing.”
He's set to start in the unpaid role immediately, working within the Department for Education.
After his brother's death, Dr Alex said his sibling had "no diagnosed prior history of a mental health condition".
He wrote in The Sun: "On paper, Llŷr didn’t look like someone who might have a mental health condition but that’s the rub — there’s no “type” when it comes to mental health and suicide."
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Watch: Dr Alex George set to train as a GP