Despite the quick departure, Keitch is not severing ties with the organisation. He will still serve as its media spokesman through to July, and will not be taking another job in the short term.
Keitch has served as chief of membership and brand, responsible for engaging with government and the direct marketing industry, since the public-facing role was created in a restructure last June.
The restructure also created a chief of operations role, which is still occupied by Mike Lordan.
Prior to the restructure, Keitch spent three years as the DMA's director of media channel development and environmental affairs.
DMA chairman David Metcalfe said Keitch had been a "tremendous asset" whom the body was "sorry to see step down", but it respected his decision.