The award-winning funnywoman will team up with presenter Jon Holmes to front the show for a week while Chris Evans is away.
The duo, who take over on 3rd October, have previously hosted one-off bank holiday shows for the station.
Hart - who has her own BBC One comedy series - said: "There aren't many people I am happy to spend the breakfast hours with, but I can't think of anyone nicer than the Radio 2 massive and my colleague Jon Holmes and his ridiculous bed head."
Holmes joked: "I'm looking forward to waking up between Miranda on one side and the entire nation on the other. That promises to be quite some party the night before."
Richard Madeley will also step in as a guest host during Evans' absence later this month.