Baker will join Matthew Fleming and Alex Johnston, the ex-founding partner of Freud Communications, as managing partner of the fund.
He has held the role of managing director, networked media, which was previously known as Sky Interactive, since January 2006. He was previously director of programmes with Sky One, Two and Three.
Baker said: "I've had a wonderful time at Sky -- they've given me so many great opportunities over the last 10 years. My new role at Fleming Media will give me the chance to use much of the valuable experience I've gained.
"I'm very impressed by the innovative work Fleming Media is developing in intellectual property development. It's a great commercial environment with a broad, all-encompassing remit and a genuine perspective on how brands and content evolve in a digital world."
Dawn Airey, Sky's managing director of channels and services, said: "James has made a significant contribution to Sky over the last decade. He has an unrivalled knowledge and passion for the business and is a much respected and loved colleague.
"We are sorry to see him leave but wish him all the success in the world as he embarks on this new venture."
Airey, herself, announced this month that she would be leaving the broadcaster in the New Year to take up the position of chief executive at start-up media company Iostar.
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