Black came to Lower Canada (present day Quebéc) in 1802 in the service of the XY Company as a clerk, perhaps encouraged by his maternal uncle and fur trader, George Leith, and probably joined the firm of Leith, Jamieson and Company, part of the XYC. He already had relatives living in Canada at the time of his arrival. At the joining of the XYC and NWC in 1804, Black "passed with the Company's organisation," and went to work for the North West Company, headquartered in Montreal. Assigned to work in the Athabasca Department (mostly in present-day Alberta) in 1805, Black served as a clerk there for fifteen years. For much of this time, he took an active role in the sometimes violent competition between the NWC and the HBC. In 1816, Black was made Wintering Partner.