Agency boss Peter Bingle said he turned down the chance to work for Robert Mugabe's regime.
Bingle, chairman of Bell Pottinger Public Affairs, made the admission to the Commons public administration select committee last week.
He told the MPs: 'We will turn down clients. We had a call from Zimbabwe asking to advise Zimbabwe. We said thank you very much, but no. It would have been a fairly malign campaign if someone had run it.'
Bingle added that when the agency is approached by an overseas client 'we would talk to the foreign office, take a view, look at whether we would want to work for that type of country or company'.
Bingle was being questioned as part of the select committee's ongoing inquiry into lobbying.