GCI would not comment on the reasons for Robinson's departure, but confirmed that he would not be replaced.
GCI UK chief executive Adrian Wheeler has taken control of the financial consultancy as CEO alongside his group role, in a bid to improve figures.
Wheeler admitted the City offering had been hit hard by the depressed M&A market - it now counts just 11 staff after a wave of redundancies over the past year-and-a-half.
'Business in the City is extremely low for us, and everybody else, and we are under mandate from our shareholders to run all parts of the business at a profit and had to take a hard look at costs and revenue,' said Wheeler.
'The idea is to run the company effectively in a business-like way while we ride out the depressed market,' he added.
GCI Financial chairman John Caine will remain in the same role at the firm.
Robinson, who was unavailable for comment as PRWeek went to press, leaves the CEO post after just eight months. He took over after GCI Financial founder Rupert Ashe quit to start up creative business services firm Madsen, Gornall and Ashe.
GCI Financial co-founder Christopher Joll also resigned earlier this year and has since founded rival City and corporate PR shop MJ2.
The raft of senior departures started in autumn 2001, with the departure of former European MD Alex Mackey.
GCI Financial was integrated into its parent group last November, relocating to GCI UK's Blackfriars offices.
The group had denied the move was a cost-cutting drive, but said it had resulted in a 'handful of job losses' (PRWeek, 30 November 2001).