Gower joined Channel 4 in January 2007 to launch the digital sales agency with a brief to attract third-party clients.
4DS currently represents more than 40 premium UK websites and has a roster of clients including Thomas Cook and BT.
Channel 4 chief executive Andy Duncan said: "4DS has been a significant innovation for Channel 4, which has previously focused solely on selling its own inventory.
"Matt has been instrumental in building this business from scratch and we are very grateful to him for his contribution. We wish him every success with his new venture."
Gower said: "I've enjoyed my time at Channel 4 and the opportunity to lead the launch and development of 4DS."
Prior to joining Channel 4, Gower was joint managing director of independent sales agency Media Run.
Between 2001 and 2006, he was commercial sales director of lastminute.com, sitting on its UK board of directors and responsible for all commercial revenue streams in UK, France, Germany, Italy and Spain, including all advertising, business development and commercial relationships.
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