After immigrating to America he came to York [Toronto] in 1833 and entered a dry-goods firm. He shrewdly concentrated on wholesaling and turned his enterprise into one of Toronto's most profitable. Eager to curtail Montréal's control of the western economy, he joined George Brown's Reformers. Their opposition to the Church of England and its Conservative friends also appealed to McMaster who, as a Baptist, wished to advance the cause of his coreligionists.
At mid-century he ventured into banking, and in 1867 played a major role in establishing the Canadian Bank of Commerce, in large part as competition for the Bank of Montreal. During his presidency the bank surpassed all others in Ontario and was second only to its Montréal rival. After his death, his will revealed his desire to further Baptist education. Having supported the Canadian Literary Institute (Woodstock College) and Toronto Baptist College, he gave his estate of nearly $1 million to establish a Baptist institution of higher learning in Toronto. McMaster University opened its doors in 1890 as an independent institution, after refusing federation with U of T.