Mr Jackson, 39, who has promised a major output overhaul, will combine his role as chief executive with that of director of programmes, as Jeremy Isaacs did throughout his period at Channel 4. He is attending the Venice Film Festival and was not present at Mr Willis' farewell party in London last night.
Mr Willis, 51, was on an annual salary of pounds 250,000 with a further pounds 22,000 in pension and benefits. His contract expires at the end of the decade, but he will not receive the reported pounds 1m golden handshake.
He held senior positions at Channel 4 for almost 10 years. He was controller of factual programmes in 1988 and became programme director in 1993. Two years ago, he accused Mr Jackson, then controller of BBC2 of being "the copycat criminal of British television" for allegedly scheduling similar programmes head-to-head.
Last night, Sir Michael Bishop, Channel 4's chairman, paid tribute to Mr Willis's contribution to the channel over the past decade. "It is his skill in leading the commissioning and scheduling team which helped the channel to deliver programmes that sustained the channel's reputation for daring and innovation, won an unprecedented number of awards around the world, and yet achieved increasing commercial success," he said.
Mr Willis, a popular figure with staff, said last night that he would miss Channel 4 "enormously". "I will miss working with all my colleagues here at Horseferry Road and all those around the world who produce and appear in our programmes."
He added that he was proud to bequeath a channel with buoyant ratings and an enviable worldwide reputation for its programmes and films "from Trainspotting to Father Ted, from TFI Friday to Secrets and Lies, from Rory Bremner - Who Else to Cutting Edge, and from The Dying Rooms to the Juris Podniek's series that captured the declining years of Soviet rule, Hello Do You Hear Us."Reuse content