Belam, a well-known blogger (writing on Currybet.net) and lead user experience and information architect at the Guardian, worked on the launch of the Guardian's Facebook "frictionless sharing app" and the local website experiment.
The consultancy - called Emblem - will focus on the media and publishing.
In an interview with Journalism.co.uk, Belam said: "I'm really interested in being able to help large organisations get to grips with digital, but I also want the opportunity to give some of my experience to smaller, newer ventures.
"I've spent most of the last 12 years or so working in the digital bubble on the side of a business that mostly thinks it does something else - whether that was TV at the BBC, a newspaper at the Guardian, or hardware at Sony - and so it will make a nice change of pace to work on purely digital things."
Belam spoke to us about why he is leaving the Guardian, the future of the news outlet and the launch of his consultancy.