Live on Studio 10, Harris shocked viewers with the news: ''I'm beyond excited to be joining one of Australia's most iconic and agenda-driving shows. The Project does news like no other program in Australia and it's exactly the kind of fun and fearless TV I love to make.''
Of his new co-host, Aly said: ''She's smart. She's warm. She's great fun. That's the trifecta for The Project. Everyone who's worked with Sarah raves about her, and I can't wait to be one of them.''
Watch Below: Lisa Wilkinson quits The Project
The team at Studio 10 also posted their own sweet tribute to social media, sharing their well wishes for their golden girl.
''We're very sad to see her go after almost a decade at the helm of Studio 10, but excited to watch her thrive in her new role. We have lots of great times and many moments to relive before she heads off at the end of the year, so stay tuned!''
Watch Below: Carrie Bickmore announces she is leaving The Project
The surprise appointment of Harris was also accompanied by additional announcements from the network, confirming that Hamish Macdonald will continue as a roving reporter during the week, with Georgie Tunny to feature on the panel every Friday night.
While the appointment of Harris seems a like-for-like replacement for Bickmore, it remains to be seen who will fill the gaps left by Helliar and Wilkinson on the panel.
Network 10 must also now address who will fill in for Harris on Studio 10, the 41-year-old host departing host having led the breakfast program since its inception in 2013.
A statement from the network also promised: ''more exciting announcements are on the way.''