Thomson started his business career as a junior associate at McLeod Young Weir in Toronto. He left the firm to enter the family business, working in a number of positions in companies controlled by the Thomson family. Thomson was manager of The Bay store at Cloverdale Mall in Etobicoke, and president of Zellers. In an effort to develop his independence, Thomson founded the real estate firm Osmington Incorporated, owned and operated outside of the Thomson empire. Osmington acquires and manages commercial real estate assets on behalf of institutional shareholders. In 2010, Osmington sold its stake in eight retail properties to the Canada Pension Plan for $336 million. Osmington is a major investor in FarmersEdge, a precision agriculture company. Osmington is also a partner in True North Sports and Entertainment, owners of the National Hockey League's Winnipeg Jets and the Bell MTS Place in downtown Winnipeg, Manitoba. Osmington is redeveloping the retail space of Toronto's Union Station. Thomson's investment activities are managed through Toronto hedge fund Morgan Bay Capital,