An update on the London Stock Exchange revealed the mutual was in the process of seeking his successor.
A spokesperson said Garner would stay at the mutual for as long as it took to find a replacement, and said he suggested it was right for the society to be headed up by someone else to take it into its next stage after he led it through Brexit and the pandemic.
David Roberts, chair of Nationwide, said Garner made an “outstanding contribution” as leader.
He added: “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.”
He said an “orderly transition” would allow the mutual to build on the success seen under Garner and move Nationwide into its next phase of development.
Earlier this year, Roberts asked the board to begin the process of choosing a new chair to replace him and ensure an “orderly succession and continuity of board leadership”. Roberts has been chair of the mutual since 2015.
The update today confirmed Kevin Parry, the mutual’s current senior independent director, was appointed deputy chair and chair elect.
Parry will assume the role in March next year and lead the process of finding Garner’s replacement.
Garner (pictured) said: “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.”
Parry added: “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.
“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.”