The Allan Shipping Line was started in 1819, by Captain Alexander Allan of Saltcoats, Ayrshire, trading and transporting between Scotland and Montreal, a route which quickly became synonymous with the Allan Line. By the 1830s the company had offices in Glasgow, Liverpool and Montreal. All five of Captain Allan's sons were actively involved with the business, but it was his second son, Sir Hugh Allan, who spearheaded the second generation. In 1854, Hugh launched the Montreal Ocean Steamship Company as part of the Allan Line, and two years later ousted Samuel Cunard to take control of the Royal Mail contract between Britain and North America. By the 1880s, the Allan Line was the world's largest privately owned shipping concern.

In 1891, the company took over the State Line (founded 1872) and was often referred to as the Allan & State Line. In 1897, Andrew Allan amalgamated the various branches of the Allan shipping empire under one company, Allan Line Steamship Company Ltd., of Glasgow. The company by then had added offices in Boston and London. In 1917, under Sir Montagu Allan, who represented the third generation of the Allan family, the company was purchased by Canadian Pacific Steamships, and by the following year the Allan name had disappeared from commercial shipping.

The 1970s British television series The Onedin Line (1971-1980) is a complex and veiled take on the Allan Line Family and their steamships.^{[citation needed]}

In 1891, the Allan Line steamer Carthaginian collided with the York River Line steamer Charlotte in the shipping channel at Baltimore, Maryland. Among those aboard the Carthaginian was the Danish-American composer Asger Hamerik. While both boats were damaged, neither sank.^{[ProQuest Historical Newspapers 1]}

In 1905, the Allan Line steamer Parisian was involved in a collision with the Albano off of Halifax, Nova Scotia. The owners of the Albano were found by the Exchequer Court of Canada to be fully at fault, according to Reports of Cases Relating to Maritime Law.^[1] The case was later appealed to Canada's supreme court.

The Allan Line fleet evolved over the course of decades, changing as new ships were added, lost at sea, sold, or scrapped:

• 
  SS Sardinian
• 
  SS Scotian
• 
  RMS Virginian

• Appleton, Thomas E. (1974). Ravenscrag: The Allan Royal Mail Line. Toronto: McClelland and Stewart. ISBN 0-7710-0720-5 (cloth)
• "C.P.R. Gets Allan Line; Report Declared to be Correct in Spite of Official Denials," New York Times. August 17, 1910.

• Allan Royal Mail Line - passenger lists and historical documents GG Archives