Having obtained a good general education in Scotland, he joined Pollok, Gilmour and Company in 1815, and in 1818 was transferred to Miramichi, New Brunswick.
In order to employ its large fleet fully in the winter months, branch houses were opened in New Orleans, and Mobile, Alabama, where the company entered the rapidly expanding and very profitable cotton trade.
He funded mechanics’ institutes, temperance societies, and orphans’ homes, and he contributed several large sums for the laying of the first Transatlantic telegraph cable in the 1850s and 1860s.
The death of his daughter, drowned in Menai Strait, Wales, in August 1869, was a crushing blow to Rankin, who had already lost four of his seven children through childhood illnesses.
According to his biographer David S. MacMillan, Rankin contributed greatly to the amazing growth of the shipbuilding and timber trades in 19th century Canada.