Platform is the intermediary lender of The Co-operative Bank and last year launched a new range of mainstream mortgage products designed for the intermediary sector.
Lee Gladwell, director of sales & propositions, at Platform said: "We are delighted to join AMI. It plays a vital role in supporting intermediaries and we look forward to forming a close and active relationship.
"There are significant issues and opportunities for the sector and we believe it is critical that lenders and intermediaries work together to promote its growth and professionalism. Being a member of the AMI strengthens our support in helping the sector achieve this."
Robert Sinclair, director at AMI said: "We are delighted to have the support of Platform at this time of challenge and opportunity. The support of forward thinking lenders, such as Platform, allows AMI to continue its work in support of the intermediary community.
"I look forward to developing closer links with the team at Platform and working together to develop a more sustainable mortgage market."
The move demonstrates Platform's continued backing for the intermediary sector and follows the recent appointment of Lee Gladwell to the Intermediary Mortgage Lenders Association's (IMLA) new board of directors.