William was born in Manhattan, New York and was the son of Alexander Gwynne. When he grew up, it is noted that he started working in a postal service in Brooklyn for his family.
He married Florence Rohde in 1907, on St. Valentine's day. Their first child was called William Thruston and born on 1909.Later, they had another child in 1911, called Marjorie.
He was last seen standing on the Boat Deck near the gymnasium, beside Chief Purser McElroy, both men died in the sinking of the Titanic. William's wife collapsed in shock when hearing the terrible news of his death.
His body, if recovered, was never identified.