Cameron is becoming chairman of the NCS Patrons "bringing together a senior cross-party and cross-sector group of patrons and ambassadors who can help NCS to reach more youngsters," he writes in a column announcing the new role in the Daily Telegraph.
Cameron resigned as Prime Minister in June after the result of the referendum on Britain's membership of the European Union. He announced he was stepping down as MP for Witney in September.
The NCS was set up in 2010 as part of Cameron's "Big Society" initiative under the coalition government. The scheme, launched with the support of actor Michael Caine, offers 16 and 17-year-olds an 8-week-programme of team building and community fostering activities, inspired by the post-war generation's national service.
The programme is meant to give teenagers "a sense of purpose, optimism and belonging," according to Cameron, and 275,000 people have gone through it since its launch.
The former Prime Minister calls NCS "one of my proudest achievements," writing in the Daily Telegraph: "NCS is building bridges across social divides, enabling young people to realise that wherever they come from and whatever their faith, background or sexuality, there is so much more that unites them than divides them."
Cameron's role will be unpaid.