Wasserman had been in the role since West One was acquired by Enra Group in 2014.
After 14 years with West One, Wasserman has left the business after a period of handover and decided to take time out before pursuing other commercial interests, the lender said.
A replacement has not yet been found, but a spokesperson said there was no set deadline for a new managing director and added the lender was taking its time to “make the right strategic decision”.
Danny Waters, CEO of Enra Group said: “Stephen worked hard to help grow our bridging division since we acquired West One.
“On a personal level I’m sorry to see Stephen depart having worked closely with him for many years, and I wish him all the very best for the future.”
Wasserman (pictured) said: “It was a very difficult decision to leave, but after much thought I decided the time was right to step aside.
“I believe Enra Group is well positioned for further growth and has a very bright future as a major force in the specialist lending market. I wish everyone all the very best for the future.”