The lender made the decision to join the trade body following the launch of its £30m fund with its trustees T Bailey.
Chief executive Paul Munford said: “We have joined the ASTL because we want to be part of the industry and we want to be part of any discussions from a regulatory funding or marketing point of view.
“Being part of the ASTL will help us to boost our profile and increase our knowledge of industry issues.”
Century Capital, owned by Munford’s Mayfair-based brokerage Mortgage Centre IFA, piloted a soft launch of the fund this summer. Following its success the £30m fund went live in October targeting sub £1m deals – most of which have a development angle in London and the South East.