The lender is set to launch in Q1 2009 under executive chairman Stephen Knight.
Stimson will be responsible for marketing, products, strategy and flow agreements.
Before joining Checkmate, Stimson was executive director, structured finance at Lehman Brothers.
Stimson was also head of product development at GMAC-RFC while Knight was executive chairman of GMAC-RFC.
Knight says: “I have known Stimson for a long time and have a high regard for his ability. He will be a valuable addition to our senior management group.”
Stimson adds: “It is fabulous to be joining an organisation with the quality of people at Checkmate. With the best team in the industry I look forward to helping to write the next chapter in the mortgage industry“.