He will be replaced by Leigh Bartlett who is currently chief financial officer.
Bloom will continue as a shareholder and non-executive director.
Masthaven was founded in 2004. Bloom built the business up from a specialist bridging lender to bank, after the firm received its banking licence in 2016.
The lender now has more than 180 staff, and has completed £1.1bn of lending while raising £1.2bn of savings from customers.
In April 2019, Värde Partners completed a strategic £60m equity investment in Masthaven.
Bloom said: “Masthaven has been a major part of my life over the past 15 years and it has been a privilege to found, serve and grow Masthaven from the early days when it was just a handful of people to the specialist bank it is today.
“I am very proud of Masthaven and how its talented employees have always striven to deliver a personal solution for our customers and intermediaries.
“We have built an incredibly strong foundation and a great leadership team. As a non-executive director and significant shareholder, I will continue to assist Leigh and the leadership team in driving Masthaven forward.”
Bartlett added: “It’s an honour and great responsibility to take over from Andrew. I would like to thank him personally for the support he has given me since joining Masthaven. I look forward to continuing to grow the bank, together with the Masthaven team, to become one of UK’s leading specialist banks in the UK residential and SME markets.”