The team, headed by Anthony James, OMG's business development director, has been set up to deal with charity clients wanting to use online marketing to promote sponsorship and gift packages during the run-up to Christmas.
Affiliate programmes for their two most recent signings, international anti-poverty agency Action Aid and The Children's Society, were launched earlier this month.
OMG currently manages online marketing programmes for a number of other charities, including Cancer Research UK, WWF, NSPCC, Childline, PDSA, the Aspinall Foundation and the Whale and Dolphin Conservation Society.
Oli Matthews, OMG's marketing director, said: "There is a huge opportunity for charities to tap into the gift market online. With more people wanting to make their present really count, ethical and alternative gift giving is growing in popularity -- so charities are increasingly using gifts as a way of generating revenue.
"Our work with major charities over the last few years has proven that affiliate marketing, in particular, can generate significant increases in revenue and help them reach and build long term relationships with supporters."