William was born on the 21st of April, 1877, in Johnson, Kansas, and unfortunately there is not much publicly known information regarding his early life. It is known that he enlisted in the US Army in 1898 and was a Private when he deployed to the Philippine Islands with Company B of the 20th Kansas Volunteer Infantry. His actions here earned him the Medal of Honor and the citation reads:

Swam the Rio Grande de Pampanga in face of the enemy's fire and fastened a rope to the occupied trenches, thereby enabling the crossing of the river and the driving of the enemy from his fortified position.

William received his Medal of Honor on the 11th of March, 1902, after being out of the Army for about three years. He later joined the Army again to serve in World War 1 where he was commissioned as a First Lieutenant until 1919. He served as the Postmaster for Kansas City, Kansas from 1921 until 1935 and William Beattie Trembley died on the 13th of January, 1952 at the age of 74. He is buried in Monticello Union Cemetery in Shawnee, Kansas.