Samuel McClennan was born to Charles and Mary McClennan in February 1845. Not much is known of Samuel before the Civil War, but in February 1864 he enlisted with the 51st PA Volunteer Regiment. The 51st was engaged at the Siege of Petersburg at the time, lasting until April 2, 1865. After Petersburg was captured, Richmond soon followed and Samuel would have been with the Regiment in the final days of the war when Robert E. Lee surrendered at Appomattox. He mustered out of the regiment in July 1865.

Samuel worked numerous jobs throughout his life after the war. In 1870 he was living in Norristown and working as an expressman. He also worked as a watchman and clerk. However, by 1909, at the age of 64, Samuel was suffering numerous health problems. He ended up in a National Home for Disabled Volunteer Soldiers in Tennessee in 1909 due to an old leg fracture, a hemorrhage, hypertrophy, and other medical problems. Despite the medical problems, Samuel lived until January 11, 1922 when he passed away in Norristown.