Stourton (right) will stay on until Webb (left) returns from the US
Justin Webb, the BBC's North America editor, is to join Radio 4's Today programme in October as Edward Stourton leaves to work on other projects.
"There isn't a more challenging job in British broadcasting," said Webb.
Webb will present the daily programme for a year, alongside current regulars John Humphrys, Sarah Montague, James Naughtie and Evan Davis.
Stourton will continue to present Today until Webb returns from his posting in Washington DC, the BBC said.
Webb, who has occasionally presented the show in the past, recently led the BBC's coverage of the US presidential election and its aftermath.
His other roles include three years as the BBC's Europe correspondent and another three as the main presenter of BBC One's Breakfast News.
Radio 4's controller, Mark Damazer, said Webb had been an "outstanding voice" on the station for several years.
"His work in the United States has been one of the joys of the network and I look forward to his arrival on Today."
Mr Damazer also paid tribute to Stourton, whom he described as "a distinguished journalist with a terrific track record in a host of Radio 4 programmes".