Charlie Crick, 16, from Bullbrook, who has a complex congenital heart disease, will help other children supported by Rays of Sunshine.
The charity helps grant wishes to children with serious illnesses, and helped Charlie meet his favourite band JLS in 2013.
Charlie has also attended several other events, including recording the song ‘Bring me Sunshine’ at the legendary Abbey Road Studios, in support of the charity’s 10th anniversary.
He said: “It is an honour and a privilege to become an ambassador for Rays of Sunshine Children’s Charity.
“They have helped so many children already, and I hope, through the things that I have had to endure, I will be able to offer support to seriously ill children and to help them realise there is always hope. Making a child smile is better than any medicine.”
His father Ted said he was proud of his son and added: “He inspires people and makes us feel humble; he always tries to help in whatever way he can.
“He has been through too much for a young person, but his determination to live a life is a lesson for many to take note of.”
The charity’s celebrity ambassadors include One Direction, Gordon Ramsay, Leona Lewis, Pixie Lott, Olly Murs, Louis Smith, Dynamo, Lorraine Pascale, Amanda Lamb and members of the former band JLS.
Jane Sharpe, chief executive of Rays of Sunshine, added: “We’re absolutely delighted to announce Charlie as an official wish ambassador – he has become an important member of the Rays of Sunshine family ever since we granted his wish.
“Everyone who meets Charlie is inspired by his courage and we are so grateful that he is now offering to use his bravery to help other seriously ill children.”