With his cousin, Louis Klein, he founded the men's fashion companies Anthony Squires [4] [5], Parini [6] and Sax Altman [7] With Eric Hurst (an optometrist) and Dino Zingarelli (a spectacle frame expert), Sinclair founded Martin Wells, the maker of fashion spectacle frames [8].
In 1968 Sir John McEwan, Minister for Trade and Industry, appointed Sinclair to the Export Development Council.
In 1972 Dr Jim Cairns appointed him to the Trade Development Council, and in 1974 he became a member of its executive.
While serving on the EDC he was a member of a small group sent on Diplomatic Good Will Missions sent to the USSR, Poland, Romania, Czechoslovakia and Japan.
He was a constant adviser to governments on both sides of politics, and for 2 years was one of 3 people who advised Prime Minister Gough Whitlam at pre-budget meetings to be used for cabinet briefings, and was appointed to several advisory committees by Deputy Prime minister, Douglas Anthony .