During his time with the Bank of Montreal, Angus was free to pursue opportunities for private investment. In 1868, he went into partnership with the future Lords Mount Stephen and Strathcona at the time that they were becoming interested in developing railways across to the Canadian West. Their ventures were largely financed by the Bank of Montreal, of which Mount Stephen was president, and as his number two at the bank, Angus was closely involved. Angus resigned from the bank in 1879, briefly relocating to St. Paul, Minnesota, to represent the group's interests there as vice-president of the Saint Paul and Pacific Railroad.