After a decade as host of the radio current affairs program AM, Eastley will join ABC News 24 as a senior presenter. He will be replaced by Trioli, currently co-host of News Breakfast alongside Michael Rowland.
Journalist Scott Bevan will take a new prime-time presenter role with ABC News 24 and will anchor major news coverage on both News 24 and ABC1.
The changes will come into effect in March with a new co-host for News Breakfast still to be decided.
The ABC's director of news Kate Torney said Eastley was "a great addition" to ABC News 24.
"He'll bring 35 years of experience across almost every editorial and presenting role at the ABC. He's one of our very best journalists and his addition to Australia's most watched news channel is another investment in the strength of its coverage and its value to a growing audience. 2014 is going to be an exciting new chapter in the development of ABC News 24."
Torney described Trioli as "a dynamic radio presenter and a formidable interviewer".
"And her addition to one of the ABC's strongest editorial teams will be a potent combination."