Zentropy Partners, which provides interactive marketing services to clients including Nestle, Unilever and Hewlett-Packard, has let McCulloch go eight months after charging him with developing its media planning and buying operations.
McCulloch, who founded interactive agency Saatchi & Saatchi Vision, joined Zentropy after working with the agency on project work for Unilever.
McCulloch said: "It was a pragmatic move to cut costs due to a shortfall on revenue targets for the media part of the business. One significant factor was that Compaq merged with Hewlett-Packard. It meant we were no longer doing media business with them."
McCulloch claimed media planner Peter Kwong was also made redundant as a result of cutbacks from the agency's media team, which he said now consisted of three staff.
"I'm looking around at the moment, but I might do some consultancy work for a while, said McCulloch, who added that he intends to continue in his digital role at the IPA.
McCulloch previously had a stint as managing director of online ad specialist i-level.
A spokesperson for Zentropy was not available for comment.