Jon Kay is the new regular presenter of BBC Breakfast from Monday to Wednesday, while Victoria Derbyshire will become joint lead presenter of Newsnight, the BBC has announced
Kay said he was "over the moon" about his new role, which begins with immediate effect.
Derbyshire, who joins Kirsty Wark from September, said she was "delighted".
BBC Breakfast and Newsnight are the corporation's flagship news and current affairs TV programmes.
Kay said: "I'm over the moon to become the new regular presenter of BBC Breakfast and I'm looking forward to bringing our brilliant viewers the very latest news each morning alongside my good friend Sally [Nugent] and the rest of the team."
He has already been filling in on the show since Dan Walker left for Channel 5.
"Sitting on the famous red sofa is a real privilege while covering the stories and issues that matter to our audience - home and abroad."
Victoria Derbyshire's role follows the departures from the programme of Emily Maitlis and Emma Barnett earlier this year.
Derbyshire said she was "so delighted to be joining the legend that is Kirsty Wark and the talented Newsnight team under new and ambitious leadership."
'Stories about people's lives'
"This is a special opportunity to take on one of the best jobs in British journalism and help shape the programme's future," she said.
"I can't wait to champion more stories about people's lives while holding those who represent them to account."
Broadcaster and journalist Derbyshire previously fronted her own BBC current affairs show, which was simulcast on TV and radio, from 2015 to 2020.
In 2017 she described the reaction to her revealing she had been wearing a wig on-air after months of chemotherapy for breast cancer.
She has previously filled in as host of Newsnight and Panorama, and also appeared on ITV's The Real Full Monty: Ladies Night - an entertainment documentary to raise awareness of breast cancer.
Presenter and newsreader Kay has worked as a news correspondent for BBC News, reporting from Portugal on the investigation into the disappearance of Madeleine McCann in 2014; and from Cape Town on the trial of Shrien Dewani.
Jonathan Munro, interim director of BBC News, said it was "fantastic" to appoint "two talented presenters to start and finish the day on two of our most important news programmes".
Newsnight editor Stewart Maclean said Derbyshire and current host Wark "will be a formidable partnership at the heart of our presenter line-up".