Nationwide chairman David Roberts and chief executive Joe Garner are both to stand down.
Garner led the society for more than five years before asking the board to look for a successor.
Under his leadership, the society grew by over 20% and significantly increased its financial strength and resilience.
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It also grew its stock of residential mortgages by £28bn.
Roberts, Nationwide’s chairman since 2015, requested that the board start the process to select a new chair earlier this year.
Roberts said: “Joe has made an outstanding contribution as leader of Nationwide. He has led the Society through the challenges of Brexit and COVID, and we have emerged in robust financial health able to focus on supporting our members as the country rebuilds from the effects of the pandemic.
“Over the last six years, the growth in our membership, mortgage lending and deposits aligned with our consistently superior customer service is testament to Joe’s focus on delivering the things that are important to our members.
“By putting in place an orderly transition, we will ensure a smooth handover to new leadership and continuity in the running of the society.”
Garner added: “Nationwide is one of the UK’s largest financial services organisations but most significantly it is mutual-owned and run for the benefit of its 16 million members.
“It is therefore a unique privilege to lead such an organisation, and our achievements are credit to our loyal and committed employees who have risen to the recent challenges of COVID so well.
“Together we have faced some of the most significant and extraordinary circumstances but have remained resolute in our focus on meeting the needs of our members.
“I believe that the society is in excellent health with a loyal membership and great commitment to working for a mutual organisation that has the interests of society and its members at its heart. The foundations we’ve laid down in recent years will enable my successor to continue to grow the Society and ensure we are ready to meet the future needs of our members. Until that point, I am absolutely focused on continuing to lead and deliver on our priorities.”
Kevin Parry, the society’s current senior independent director, has been appointed deputy chair and chair elect.
Parry said: “Nationwide Building Society has been part of the UK’s economic and social fabric for over 150 years, and I’m honoured to be given the opportunity to help shape its future.
“I intend to work with my colleagues to engage all our energy and experience to continuing the development of the business in accordance with the principles of mutuality that deliver great service and value for our members.
“There will be a transitional period into the role, but I’d like to thank David at this point for his dedication and commitment to the society over the last seven years.
“It is in no small part thanks to him, and to Joe, that we move into the future with confidence and certainty.”