Samuel was born on the 23rd of January 1869, in Belfast, Ireland, and emigrated to the United States at the age of seventeen. He became a naturalized citizen twelve years later in 1898 and he had enlisted in the US Navy in California. He was a Coal Passer when he deployed to China in support of the Boxer Rebellion and his actions there earned him the Medal of Honor. The citation reads:

In action against the enemy at Tientsin, China, 20 June 1900. Crossing the river in a small boat while under heavy enemy fire, McAllister assisted in destroying buildings occupied by the enemy.

Samuel was one of the three members selected by Corporal Edwin Appleton to cross the river and destroy buildings that were being used as cover by enemy snipers. Samuel McAllister died at the age of 34 on the 13th of December 1903, and he was buried at sea from the USS Wisconsin, between Japan and Hawaii. His Medal of Honor is located at the Naval Historic Center in Washington DC.