Lygo, who was director of television, will have line-management responsibility for the group's portfolio of TV channels - Channel 4, E4, More4 and Film4 - and for cross-platform commissioning areas such as acquisitions, education and film.
He will also take on the development of new 4-branded digital TV channels and an active role in overseeing the development and commissioning of content for Channel 4's services on new digital platforms, including online, mobile and 4Radio, if it wins its bid for the new digital multiplex.
Bellamy is set to return to Channel 4 after a stint as controller of BBC Three and will report to Lygo.