Most recently, Mullaney was working as a consultant at Resolution.
Before that he was involved in a management buyout of Oasis Television, where he acted as managing director for four years. He has also worked for Editworks and M2.
David Barrett, senior vice president of business development said: "We are delighted to have Gareth on board. I have known of Gareth for many years and have always been impressed by his motivation, enthusiasm and passion for the business.
"I will enjoy working with him and the company will benefit from his considerable expertise."
Commenting on his move Mullaney added: "There are a lot of really exciting changes happening at Ascent at the moment and it's a fantastic time to be joining such an innovative company, both creatively and technically."