The Cardiff-based business was established in 2013.
Optimum Credit have announced £1bn of lending since they wrote their first loan in 2014.
Sam Marshall (pictured), chief executive officer at Optimum Credit, said: “This is a fantastic milestone for us and something of which all of us at Optimum Credit are very proud.
"When we started up the company, we set out to become the biggest second charge lender in the UK, a target we achieved very quickly.
"Our acquisition by Pepper Money will enable us to continue to grow, and we look forward to further successes in the future.”
“Despite some uncertainties in the lending market given the ongoing Brexit discussions, we have found the second charge market to be very buoyant, with a record month of new origination for Optimum in September 2019.”
The Cardiff-based business was established in 2013 and announced an acquisition by Pepper Money at the end of 2018.
