He will become a non-executive director of the group after working for the company over the last 15 years.
Preece will also provide additional time to MAB in a consultancy capacity.
He remains a significant shareholder of the group with a 2.98% shareholding in MAB.
Preece became part time two years ago, delegating some of his operational responsibilities to other members of MAB’s senior management team.
It comes after MAB recently appointed Don MacPherson as chief commercial officer, to help the group take advantage of market opportunities.
Chief executive officer Peter Brodnicki said: “I would like to thank David very much for his long-standing commitment to MAB, he has been an extraordinary COO, board director, mentor, and friend.
“David has helped us navigate challenges with confidence and certainty, but as importantly to be pioneering, which is fundamental to MAB’s DNA.
“His Lifetime Achievement Award at The British Mortgage Awards in 2016 (pictured) demonstrates exactly how highly thought of David is, not just at MAB, but also by many across our industry.
“I am delighted that he will remain on the board as a non-executive director, and that we will continue to benefit from his wealth of experience and passion for the business.”
MAB chairman Katherine Innes Ker added: “I have long valued David’s wise counsel, deep insights, judgement, and thoughtfulness, combined with his warm sense of humour.
“His commitment to MAB is evident, and I am delighted that he will remain on the board as a non-executive director upon his retirement.”