Sinclair teaches Philosophy twice a week at the London School of Economic Science.[13]
He has been the chairman of a number of charities, including the School of Communication Arts, The Designers and Art Directors Association, The Art Academy and the Independent Educational Association.[14] He was briefly chairman and a trustee of the Tony Blair Faith Foundation.[15][16]
He is a governor St. James School,[17] a senior member and lecturer in the School of Philosophy,[18] and for ten years, was organiser of the School's annual event known as Art in Action at Waterperry. [19] He was a founding shareholder in the Dukes Education group of companies[20]
He is the author of the book, Brutal Simplicity of Thought.[21] The thesis of Sinclair's book is to strip creative thought back to ensure that advertising campaigns have maximum impact in their simplicity.[22]
Along with his wife Jacqueline, Sinclair authored the children's book Faces, Faces, Faces, published by Penguin Random House.[23] The story explores the world of faces that children see in inanimate objects.[24] The inspiration behind the book comes from previous artwork that his wife created, as well as her enjoyment of the children stories that Sinclair told their own children.[25]
Sinclair was appointed Commander of the Order of the British Empire (CBE) in the 2017 New Year Honours for services to advertising.[26]
Sinclair created and co-wrote the 1988 British television comedy series for children News at Twelve. The series followed 12-year-old Kevin Doyle (Ewan Phillips) and his nightly "news bulletins" about the events in his life (and some events from his imagination).