Saunders worked at WCRS for ten years and was appointed to the strategy role last year. During his time at the agency, he took a leading role on the relaunch of Hutchinson 3G's 3 brand in the UK.
Previously, Saunders was the head of strategy, overseeing the 118 118, Mini and Orange accounts. He became the agency's youngest-ever board account planner in 2001 after his part in winning Vodafone's pan-European business.
Saunders, who will report to Channel 4's director of marketing, Polly Cochrane, replaces Rufus Radcliffe, who was promoted to head of marketing for Channel 4 last year.
In his new role, Saunders will be in charge of all on- and off-air marketing for Channel 4's digital channels and will oversee marketing activity for any future digital television channels.
Cochrane said: "Saunders is one of adland's brightest talents. Our digital services are among TV's most distinctive and admired brands and it requires someone of his pedigree to maintain and develop their stand-out positioning in a very crowded marketplace."
She added: "This appointment completes a restructure of the Channel 4 marketing team in line with the three legs of our future growth strategy - core channel, multichannel and new media."
After moving on to Freeview in May 2005, E4 increased its share of the multichannel market by 88 per cent. More4 has the highest ABC1 profile of any digital channel since launching in October.