Founded in Montreal, Quebec, as The Sun Insurance Company of Montreal in 1865 by Mathew Hamilton Gault (1822-1887), an Irish immigrant who settled in Montreal in 1842, its operations actually began in 1871. By the end of the 19th century it had expanded to Central and South America, the United States, the United Kingdom, West Indies, Japan, China, India, North Africa and other international markets. During the next five decades, the company grew and prospered, surviving the difficulties of World War I and the large drain on its finances through policy claims arising from the large number of deaths caused by the Great Flu Epidemic of 1918.
The company's original Dominion Square building in Montreal was built in 1918. Capping a Montreal construction boom that began in the 1920s, the company completed construction of the expansion of its headquarters with its new 26-storey headquarters north tower in 1933. Although the head office of the Royal Bank of Canada on St. James Street was taller by several floors, the Sun Life Building was at the time the largest building in terms of square footage anywhere in the British Empire.
Chartered in 1865, its traditional base business worldwide remains life insurance, but it now also has significant asset management operations. In 1919, it was the first Canadian company to offer group life insurance. Having begun its first US operations in 1895, the company sold its first group life plan in the U.S. in 1924