He was a co-founder of Universal McCann in 1995 and has held the managing director position at the agency and been a director of Magna Global UK.
Shaw has gone on six months' gardening leave during which he will not be allowed to pitch for Universal McCann clients should he form a start-up agency.
His responsibilities will be assumed by worldwide chief executive officer, Murray Dudgeon, until a suitable replacement can be found.
Shaw's resignation marks the second senior departure in recent month from the two media networks owned by the troubled Interpublic group.
Philippe Bernard, EMEA president for Universal McCann's sister network Initiative, also left the group late last year.
Bernard was replaced by Jerry Hill, UK and Ireland chief executive and Dirk Wiedenmann, CEO for Germany, Austria, Switzerland and the Netherlands.