The eliminated X Factor singer will fill in for Richard Arnold while he takes a break from the ITV morning show.
Clark will front the daily showbiz slot at 7.50am with Aled Jones and Lorraine Kelly from December 3-7.
Richard Arnold will return the following week after taking a holiday following his stint on the BBC's Strictly Come Dancing alongside his ITV duties.
Clark said of his role: "I can't believe it! I only left X Factor a week ago and now I'm joining Lorraine and Aled on the Daybreak sofa!
"I'm a massive fan of the show and it's going to be so much fun sharing all the showbiz news and gossip with the nation each morning.
"I'm looking forward to keeping Richard's seat warm while he's swanning off on holiday, but I won't be asking for any dancing tips just yet!"
Richard Arnold added: "The wonderful thing about this hurly burly business we call show is that you know ultimately you will one day be replaced by someone younger, thinner and in this case much taller than you.
"I wish Rylan all the best in his new role at Daybreak."
Rylan Clark is said to be in high demand following his stint on The X Factor, including links with The Only Way Is Essex, Celebrity Big Brother and next year's Eurovision.