He will be replaced by the company's executive producer Kai-Lu Hsiung, who is set to streamline the roster of directors and lease out RSA office space in the midst of an increasingly tough climate.
"I am very honoured to be asked to step into Adrian's shoes and am looking forward to the challenge. RSA has always been, and continues to be, one of the flagship production companies in the UK industry and I intend to keep it that way," she stated.
Hsiung has been at RSA for more then ten years, working her way up from production manager to producer for directors such as Hugh Johnson and Laurence Dunmore.
In August 2000, she was appointed to the role of executive producer and worked alongside Harrison.
Harrison, meanwhile, is leaving to pursue other opportunities but will remain as a consultant to the company for the transition period.
"It has been a fantastic 15 years of my life, but the time is right to move on and I wish the company only the very best for the future," Harrison said.
Debbie Garvey, formerly RSA's head of production, becomes the deputy managing director.
The company's founder, Ridley Scott, said: "Adrian has done a fantastic job at RSA Films, bringing in new talent such as Chris Cunningham and Dawn Shadforth, and he will be missed."