He was born in London, England in 1824. He studied at Eton College and came to Lower Canada in 1841 as an employee of the Hudson's Bay Company. Simpson served with the company until 1864, serving as a the last factor for the post at Sault Ste. Marie, where he settled after his retirement. His cousin, George Simpson, was a governor of the Hudson's Bay Company. In 1870, Simpson acted as guide and interpreter for the Red River Expeditionary Force. In 1871, he was named Indian Commissioner for Rupert's Land and resigned from his seat in the House of Commons. Later that same year, he arranged Treaties 1 and 2 with the Ojibwa and Swampy Cree Nations in southern Manitoba.