The 28-year-old will take over from Fern Britton, who steps down after 10 years on Friday.
Holly is looking forward to working with Phillip Schofield, 47, her co-host on Dancing On Ice.
'This Morning has always been the ultimate dream job for me,' she says. 'To spend my days sat next to Phil on the sofa just makes it that bit extra special. Now I just can't wait for it all to start.'
Holly, who has already guested on the show, will start in September and is believed to have beaten the likes of Davina McCall, Fiona Phillips and Ruth Langsford to win the role.
'She is a massive fan of the show, a brilliant broadcaster, a fun person to be with and she proved on the morning she spent here filling in for Fern that as presenter, she completely understands the programme,' adds Phillip.
'I'm really excited and can't wait to come back with her after the summer.'
Where next?- Look at Fern's dramatic weight loss
- All our Holly Willoughby stories
- Look at all of our Fern Britton content