Sanderson leaves Telegraph Group after 18 years as it conducts a reshuffle of its senior management team.
Details of the management restructure are still being finalised and a replacement for Sanderson is likely to be part of the changes.
Sanderson said: "I believe I have been good for the company and the company in turn has certainly been wonderful to me, but it's the right time for me to move on."
Dan Colson, deputy chairman and chief executive of Telegraph Group, said: "Len Sanderson is one of the advertising sales industry's great professionals. He and his team have done a magnificent job of expanding the Telegraph's position and we wish him continued success."
Sanderson was the brains behind Apollo, the planned joint sales house for the Telegraph Group and Mirror Group, which failed to get off the ground last year.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the Forum here.