A process has begun to identify and recruit a successor for when Mr Tarran relinquishes the position by the end of the year.
Curtis Banks says Mr Tarran will retain his current responsibilities until the process is complete “to ensure a smooth transition.”
Mr Tarran has been involved with Curtis Banks since its foundation nearly a decade ago and was appointed as chief financial officer in 2012.
The firm says he has played an important role in the significant growth of the group and also the successful IPO of the business in 2015.
Will Self, chief executive of Curtis Banks, said: “The board is grateful for Paul’s huge contribution to the Curtis Banks Group.
“He has played an important role as chief financial officer during a period when the business has grown from a start-up to one of the UK’s largest independent SIPP operators.
“Paul has agreed to provide the support needed to ensure that a smooth transition takes place after a suitable successor has been identified.”
Mr Tarran said: “I’ve hugely enjoyed my near 10 years with Curtis Banks and I’m immensely proud that it has grown into one of the UK’s market leading pension companies during that period.
“The time is now right for me to take a step back from the business as the board continues to focus on the opportunities ahead.
“I look forward to working with my successor to ensure a smooth transition.”