From next month she will help out on an ad hoc basis with Cub and Beaver Scouts in North Wales, working with boys and girls aged from six to ten.
Girls have been allowed in the Scouts since 1976. Last year 4,330 joined, compared with 3,796 boys.
According to the Scout Association, Kate will lend a hand with the day-to-day working of her packs as well as activities including running games, teaching first aid and helping out with cooking and campfires.
A St James's Palace spokesman told the Mail that the duchess had been keen to become involved as she "loved the idea of Scouting and working hands-on with children" and felt it tied in with her own interests and hobbies, particularly the outdoors.
More importantly, she hoped to raise public awareness of the dire shortage of adult volunteers.
Although there are more than 500,000 Scouts in the UK, there is a waiting list of more than 33,500 children due to the lack of helpers.
Adventurer and Chief Scout Bear Grylls welcomed Kate's involvement, saying: "The duchess has an incredibly busy life, which makes it all the more inspiring that she has chosen to volunteer alongside us." Details of the duchess's new role were revealed by St James's Palace yesterday alongside four other charities of which she has agreed to become patron.
All reflect her interests in the arts - she gained a 2:1 in History of Art at St Andrews University - the promotion of outdoor activity and supporting people in need, particularly young children.
Following the lead of her husband, Prince William, she says she wants the chance to become intimately involved with causes close to her heart rather than spread her attentions too thinly.
She will embark on her new solo royal role while her husband is stationed with the RAF in the Falklands next month.
- THE DAILY MAIL