Barry, host of the popular Saving Grace podcast, said she was “excited” to present a series of shows throughout the year, starting in September.
“You’ll hear some of my favorite songs, we’ll talk to some really interesting guests, and, as always, in true HK Barry style, I promise lots of humor, mayhem and awkward stories,” she added.
Marlow will take over from O’Leary and co-host alongside Vicki Hawksworth from Friday to Sunday from 10.30am to 1pm BST.
The popular content creator, who narrated BBC Three’s I Kissed a Girl, previously hosted Early Breakfast last summer.
Marlow said she was “really excited to be joining the Radio 1 family” and hoped to “capture your ears and not your eyes because this is radio”.
Presenting duo Danny Milo and Rosie Madison will take over the Early Breakfast spot from McCullough, who said leaving after “the most incredible 6 years at Radio 1” was “such a difficult decision”.
Northern Irish presenter McCullough, who took part in I’m a Celebrity…Get Me Out of Here! in 2024 thanked listeners who had listened to him over the years but felt it was “time for a change.”