Hytner, who is one of the most experienced marketers in broadcasting, joined Channel 5 in 1998 as director of marketing and new business and a member of the board. He was previously marketing director at BSkyB.
Hytner will be responsible for on- and off-air marketing at the commercial TV network and will report directly to ITV chief executive Stuart Prebble.
Prebble said, "I am delighted that Jim is joining us in this key role. His experience of both multichannel and network broadcasting will be invaluable to ITV as we extend our brand across a family of channels and services."
The ITV network has announced a series of changes in an attempt to strengthen its brand in an increasingly competitive market. The first change is the rebranding of ONdigital to ITV Digital, which takes place today.
Most significantly, it has announced the renaming of its flagship terrestrial channel ITV to ITV1, which will happen later this year.
A new premium pay-TV sports channel, ITV Sport, is launching on August 11.