Breon Corcoran, the boss of Paddy Power Betfair, is to step down after 16 years with the bookmaker.
He will be replaced by Worldpay chief executive Peter Jackson, who has been appointed following a "rigorous and extensive succession process", the company said.
Mr Corcoran, a gambling sector veteran, was instrumental in the £7 billion merger between Paddy Power and Betfair, which he previously headed.
He said: "This was a very difficult decision to make, and there is never a good time to leave, but this is the right decision for me and my family, and following the successful completion of the merger integration it is an opportune time for the business too."
Paddy Power Betfair paid tribute to Mr Corcoran's role in moving the business to digital and in developing a mobile offering.
Prior to Worldpay, Mr Jackson was chief executive of Travelex Group from 2010 until its sale in 2015.
In 2016 he led the innovation at Banco Santander and, between 2002 and 2010, he held a series of roles in the retail bank at Lloyds Banking Group and HBOS.
He has also been a non-executive director of Paddy Power Betfair since 2016.
The firm, which is to announce its half-year results on Tuesday, will report revenue growth of 9% and underlying earnings up 21%.
It will also confirm that trading is in line with expectations and provide guidance for full-year 2017 underlying earnings of between £445 million and £465 million.