The Westlife singer will front the interactive segment of the ITV1 daytime show throughout the summer.
© WENN
© Twitter / Caroline Flack
Matt Johnson and Stephen Mulhern will stay as the main 'Hub' hosts while Only Way Is Essex star Gemma Collins and The X Factor's Johnny Robinson will also appear.
"I've always enjoyed This Morning, so I was delighted when I got the call to be part of the team," he told The Sun.
"The Hub is such a great way to interact with viewers discussing different topics - some serious and some light-hearted. I've also heard that it is a lovely team there, so I'm really looking forward to sharing the screen with Eamonn and Ruth."
This Morning executive producer Karl Newton said that Egan was "amazingly talented".
He added: "Our viewers will be in for a TV treat when he takes over 'The Hub'. He is sure to brighten up our overcast summer."
Kian Egan has also been filling in for Olly Murs by co-hosting The Xtra Factor with Caroline Flack during the Boot Camp stage of the show.
Westlife played their final concert together in Dublin last month.
