Ratcliff, who was formerly head of viewer research and insight at Five, has been reappointed to fill a void left in the network's marketing department from the departure of marketing director Jane Scott last October.
He will report to Lisa Opie, Five's managing director of content, who took over responsibilities for on- and off-air campaigns for the broadcaster after Scott left.
Opie said: "[Carl] has worked here before and understands Five's DNA and the tremendous opportunities and challenges that lie ahead.
"[He] will be a tremendous asset as we seek to create an increasingly well defined and resonant identity for the Five family of channels."
Ratcliff first joined Five in 2004 from TBWA\London. He left the network in June 2006 to join Emap as head of brand strategy development, then joined Lowe London in August last year.
Ratcliff said: "I'm so excited about the prospect of revitalising the Five brand and working with Lisa.
"The time is ripe for Five to play differently to the competition -- to instil in viewers a sense of purpose, difference and good old fashioned entertainment."
Five has seen a number of comings and goings of senior staff in recent months with the departure of Five's director of programmes Jay Hunt in December, after less than a year.
Hunt returned to the BBC to take up the job of controller of BBC One, succeeding Peter Fincham who resigned over the Queengate affair.