Clements joined the company as director of content in 2008 and has since worked to create a multi-genre production company supplying major UK networks and international customers.
A process is now in place to appoint a successor, according to the company.
Simon Pitts, CEO at STV Group, said: “As we embark on a new growth strategy for the business, the time is right for fresh creative leadership. Alan’s legacy is an STV Productions that is very well placed to meet the surge in demand for Nations and Regions programming, with a highly talented and capable team and a healthy pipeline, including two new drama commissions for BBC1.
“He leaves with all our thanks for everything he has accomplished and our very best wishes for continued success in the future”
Clements said: “I am sad to be leaving the great team at STV Productions but delighted I leave the company in such good shape. Entertainment, led by audience favourite Catchphrase, is booming.
“Factual continues to perform brilliantly, from the juggernaut of Antiques Road Trip to the impact of Ross Kemp in Barlinnie. And the drama is back with The Victim currently filming and Elizabeth Is Missing commissioned.
“I’m so proud of the fact that STV Productions will be the biggest indie in Scotland in 2018 and I wish all who work there all the very best for the future.”