Anne Richards, chief executive of M&G Investments, is to take up a role as chief executive of Fidelity International later this year.
Richards, who has 26 years of asset management experience, will join Fidelity in December 2018, reporting to chairman Abigail Johnson.
Currently chief executive at M&G Investments, a role she assumed in June 2016, Richards will step down from the board of M&G on 10 August.
Prior to joining M&G, she was global chief investment officer and head of EMEA at Aberdeen Asset Management.
John Foley, chief executive of M&G Prudential, will take on the additional responsibilities of becoming chief executive of the key regulated entities of M&G and Prudential UK.
Clare Bousfield, currently chief executive of Prudential UK, will become chief financial officer of M&G Prudential.
M&G said the changes "reflect the growing integration of these business units over the past year and will prepare M&G Prudential to operate as an independent business".
Following former Fidelity president Brian Conroy's announcement that he was leaving in February, Simon Haslam has been in the role on an interim basis, which will continue until Richards arrives.
Richards said: "This is an exciting opportunity to lead an international company as it moves into the next stage of its growth plans. Fidelity is an admired global brand with the potential to lead the market as individuals recognise the need to take ever-greater control over their financial security."
Johnson said: "Anne will assume responsibility for Fidelity International at an important time in its near-50 year history.
"Our ambitions to broaden and deepen our relationship with our clients; innovate in product development and solutions design; and to continue to develop our investment platform and workplace investing businesses have never been greater.
"I am very confident in Anne's abilities to lead the company in this exciting period of future development and growth."
Foley added: "These changes simplify the way we make decisions, improve accountability and align management capabilities with M&G Prudential's future needs as an independent listed business.
"I would like to thank Anne for her important contribution to M&G during a period of significant change. She leaves the business well positioned, with great performance for clients, strong positive asset flows and profitable growth for shareholders."