The lender follows Abbey for Intermediaries, Barclays, Lloyds TSB and NatWest who are also associate members of AMI.
Robert Sinclair, director of AMI, said: “As AMI moves to a new independent future, the support of all the major lenders will be an important aspect of the success of the trade body.
“Although predominantly funded by its members, this commitment from Nationwide exemplifies all that is good about our market. We need to work together to ensure that we all have sustainable futures and our customers get even better outcomes.”
Ian Andrew (pictured), managing director, group intermediary sales at Nationwide, added: “We are looking forward to working with Sinclair and his fellow AMI directors during this important time in the evolution of the intermediary market.”