The move became inevitable following his appointment as an adviser to the Premier League, the body which negotiates deals with TV companies, he says. Having already negotiated BSkyB's deal with the League to screen live football, Mr Chisholm said he "couldn't sit on both sides of the table".
His spell at the helm of BSkyB from 1990 to 1997 saw it emerge as the dominant force in football broadcasting, a position now being threatened by the Office of Fair Trading's court case and the rise of digital television.
BSkyB is in the process of selecting a new chief executive after Mark Booth, who replaced Mr Chisholm, said last month that he will leave to take charge of a new technology investment fund financed by News Corp. The CEO will be chosen from outside the company and is expected to be named within weeks.
Mr Chisholm said: "It's an amazing company. I loved every minute of my association with it."