Thomas George Shaughnessy, 1st Baron Shaughnessy, KCVO (6 October 1853 – 10 December 1923) was an American-Canadian railway administrator who rose from modest beginnings as a clerk and bookkeeper for the Milwaukee and St. Paul Railroad (a predecessor of the Chicago, Milwaukee, St. Paul and Pacific Railroad) to become the president of the Canadian Pacific Railway, serving in that capacity from 1899 to 1918.

He was the son of Irish Catholics, Lieutenant Tom Shaughnessy (1818–1903), "one of the shrewdest detectives and patrolmen" in the early Milwaukee Police Department, and his wife Mary Kennedy (1826–1905).

He is described by E. A. James, Van Horne's private telegrapher, as "a fashionably-dressed, alert young man, sporting a cane and giving general evidence of being what we call a live wire.

"[2] The perpetually well-dressed perfectionist Shaughnessy (who appears to have been obsessive-compulsive as well; he obsessed over cleanliness, washed his hands repeatedly every day, and as president would refuse to share an elevator with anyone else[3]) became known for tight cost controls and a meticulous scrutiny of purchases and other expenditures.

He delighted in tracing even minor transgressions and then publicly humiliating the perpetrators, usually in writing to ensure that the information became a part of the permanent record.

Even the company's most trusted contractors and senior officials were exposed to his wrath if, in their efforts to get necessary work done on time, they paid prices higher than was deemed appropriate or if they failed in any other way to follow his system.

[4] He also managed expenditures by delaying payments as long as possible on whatever excuse, to the extent permitted by law and practicalities: a practice which is credited in most histories of the CPR as being in part responsible for the ability of the line to stay afloat, particularly during the period in the early months of 1885, when the very difficult section of the line along Lake Superior was being financed by the faith and credit of the corporation.

During his presidency, the Canadian Pacific's steamship services, first domestic, then from Vancouver to Asia (the Empress Line), then trans-Atlantic, were steadily expanded and upgraded, eventually making this railroad one of the world's major shipping owners as well.

To promote tourism and passenger traffic, new or existing CPR-owned hotels, chalets and mountain camps were expanded or built in from the Maritimes to Victoria, each held to Shaughnessy's meticulous standards for cleanliness.

The CPR under Shaughnessy controlled the Consolidated Mining and Smelting Company of Canada and The Crow's Nest Pass Railway.

When Shaughnessy urged, "Fix the channels of Canadian trade eastward and westward," it was immediately pointed out that this policy was in accordance with the financial interest of his railway.

Though reduced from its original size, it was declared a National Historic Site of Canada in 1974 and is now part of the Canadian Centre for Architecture.