After leaving the HBC, he started an independent store at Fort Garry, with the blessing of the HBC. The HBC were often unable to provide enough goods for the growing settlement and McDermot was able to import his goods on HBC ships through York Factory. McDermot's friendship with Governor George Simpson proved to be extremely profitable. He was allowed a special license to trade furs to prevent furs from being traded at the American fur trade post at Pembina, North Dakota, and was granted many contracts from the HBC. In 1839 he was made a member of the Council of Assiniboia. He was part of a committee on the council which was responsible for the construction of roads and bridges, surveying, the operation of ferries, and public improvements.