The comic, played by Leigh Francis, will take over the duties from current editor Adam Vandermark. The role will see Lemon choose guests, news items and take charge of the show's running order for the February 14 edition.
"Keith was hugely popular with viewers when we gave him his agony uncle slot and has become a firm part of the This Morning family," Vandermark said. "I thought it would be a fun idea to go one step further and give him the whole show!
"Keith has what you could say is an interesting take on life, so who knows what guests he will choose, or how the fashion or cookery will be produced. Expect the unexpected...I'll be around only to make sure we stay on air!"
Meanwhile, a show insider commented: "Keith is full of ideas of what he wants to do that day and is keen to get some of his favourite celebrity guests on that he can banter with. The studio crew are preparing themselves for his guidance and even Phil and Holly are currently wondering what he'll dress them in let alone what he'll get them doing... it'll certainly be a show you wouldn't want to miss."
> ITV1 'holds urgent This Morning talks'