MD Donna Zurcher confirmed the agency is not going to replace De Souza when he leaves at the end of the month, handing his responsibilities to technology head Barbara McCall as the two practices merge.
McCall previously acted as a director of the corporate practice prior to taking on the tech role last December when her predecessor Simon Quarendon quit (PRWeek, 14 December 2001).
The combined division will count around 27 staff.
De Souza - a former director of the then Bell Pottinger Good Relations - is leaving the agency after two-and-a-half-years to launch his own firm.
He declined to comment on the yet-to-launch consultancy, but said he 'felt the time was right to set up my own agency and work for myself'.
His departure coincides with the announcement that group head of healthcare Charles Butler is to leave by the end of the year. Zurcher said Butler, who has worked at Ogilvy for over seven years, is leaving to take a career break. The agency is yet to decide if he will be replaced.