Holly Willoughby will co-host I'm A Celebrity... Get Me Out Of Here! with Declan Donnelly in the next series.
The This Morning presenter said she "couldn't be more excited to have been asked to stand alongside Dec for the next jungle adventure".
The 42-year-old has been undergoing rehab since March.
In a statement, Willoughby said her stint on the ITV show would not be permanent and she was not filling Ant's shoes, but just keeping them "warm for a little bit."
She continued: "I love Ant and want to send him my best wishes and support for a continued recovery."
Willoughby added she is "a huge fan of 'I'm a Celebrity' and actually feel like I've won a competition to go and hang out on my favourite show!
"When is it a good time to tell Dec I'm scared of everything that moves?!"
McPartlin's recovery is said to be "going very well", but the star said "for that to continue, having spoken to Dec and ITV, I have made the decision to take the rest of the year off.
“I’d like to thank both Dec and ITV for their continued support and I look forward to getting back to work in the new year.”
Willoughby's soon to be co-host, Donnelly said he was "hugely grateful to Holly for agreeing to accompany me to Australia this year.
"She was at the top of my list and I'm thrilled she said yes.
"It will be a different kind of series but we will try our best to ensure it is no less fun and eventful for our loyal viewers.
"I am also pleased to hear Holly is scared of everything.
"I am almost stupidly excited at the thought of watching her during the eating trials!"
ITV's director of television Kevin Lygo praised Willoughby as a "brilliant presenter with a wicked sense of humour who has always enjoyed a great friendship and rapport with Ant and Dec - I have no doubt she will take to Jungle life, if not the critters, really quickly."