Courtney Hughes will help front the campaign to encourage people to give time or money to charity on Tuesday, 29 November.
Five years ago, when Hughes' great grandmother was in hospital at Christmas, she was inspired to buy presents and encourage others to donate to give gifts to fellow patients. The campaign has grown, working with charities, schools and businesses, and last year saw 4,000 presents donated.
Hughes was chosen as the face of #givingtuesday by a panel of judges including journalists and figures from the charity sector.
She said: "It is a real honour to have been chosen and something I never expected. It has made it all the more special to me that I found out I had been picked to be the #givingtuesday champion on what would have been my great-grandmother's birthday."
The Charities Aid Foundation (CAF), which provides a variety of financial and other services to both the charity sector and donors, created the first official UK #givingtuesday in 2014. More than 1,400 charities and businesses, and a wide range of celebrities, rallied around the cause in the UK in 2015, as a Guinness World Record-setting total of £35m was given away globally over the 24 hours.
CAF is now working on opportunities to profile Hughes in the media ahead of 29 November.
Hannah Terrey, head of policy and campaigns at CAF, said: "Courtney is a fantastic example of what #givingtuesday is all about. "This is a day to shine a light on the countless good deeds people do every day to make life that bit better for others.
#givingtuesday began life in the US in 2012, and was staged on the Tuesday following both Black Friday – the day after Thanksgiving and a important day for US retail – and the more recently coined Cyber Monday.
The day now runs in more than 70 countries around the world. UK partners include Morrisons, Sainsbury’s, the Financial Times, Royal Mail, London Zoo, Sue Ryder, Cancer Research UK, the RSPCA and the NSPCC.