Jameela Jamil will become the first female solo presenter of the Radio 1 chart show after Reggie Yates announced he was leaving the station.
Yates, who is leaving to concentrate on his TV work, is joined by Vernon Kay who also announced his departure.
Kay - the husband of Strictly Come Dancing presenter Tess Daly, with whom he has two daughters - said: "I've had an incredible nine and a half years at Radio 1 that has exceeded all of my expectations, it has been a fabulous experience and I've loved the weekends I have spent with my listeners.
"However, when I was offered a contract extension I thought long and hard, but after 12 years of working weekends with CBBC, T4 and Radio 1, I felt it was the right time to leave as the girls are now both in school so weekends are more precious than ever."
Jamil, who will take over when Yates leaves at the end of the year, said: "I am absolutely delighted and honoured. I'm fully aware that I have big shoes to fill and am so excited to get started. I've grown up listening to the official chart so I cannot thank Radio 1 enough for the amazing opportunity."
The chart show currently pulls in an audience of around 1.5 million.
Yates, who has presented the show for five years, said: "I have absolutely loved my time hosting the Chart Show. It's been a privilege to deliver to the nation the weekly No.1 song, but after 10 years at Radio 1/1Xtra I am looking forward to focusing on other projects and new challenges."
Other changes see Matt Edmondson, who currently presents a Wednesday night comedy show, present a new show on weekend mornings from 10am-1pm.
He said: "I am delighted that from January I'll be spending my weekends sandwiched between Gemma Cairney and Huw Stephens - it is literally a dream come true, although of course in my actual dream everyone was wearing fewer clothes."
His comedy show will be taken over by comic Tom Deacon.
The Sunday night request show will be presented by YouTube duo Dan and Phil who have made a name for themselves with a series of comic videos online.
Radio 1 controller Ben Cooper said: "I'd like to thank Vernon and Reggie who have both been excellent ambassadors for Radio 1 and Radio 1Xtra during their ten years with us. I wish them all the very best.
"I'm excited by our brand new shows, which will appeal to the smartphone generation with our audience able to listen, watch and share Radio 1's great content."