Thomas Mullin was born on 26 August 1891 in Maxwelltown, Dumfriesshire, Scotland. He was the son of Charles Mullin (b. 1863) and his wife Mary Jane Gunyon (b. 1864).
His father was native to Dumfriesshire and his mother to Troqueer, Kirkcudbrightshire, and he was apparently their eldest child. He had four known siblings: John (b. 1894), Ellen Jane (b. 1897), Annie (b. 1899) and Eva (b. 1901). Thomas was educated at St Michael's School in Dumfries and may have been acquainted with bandsman John Law Hume, also a pupil.
Thomas appears on the 1901 census of Scotland living at 149 St Michaels Street, Dumfries and his father is described as a turner (in a mill). Thomas later became a pattern weaver in the same mill as his father.
When Thomas appeared on the next census, taken in 1911, he was by now living in Itchen, Hampshire at 12 Onslow Road, the home of his aunt Margaret Beattie, and he was described as an apprentice pattern maker in the shipbuilding industry. His parents had died within a short period of one another and his younger siblings remained in Dumfriesshire in the care of his maternal grandmother Ellen Gunyon. Later, Thomas apparently left the weaving industry due to failing eyesight.
When he signed-on to the Titanic in Southampton on 6 April 1912, he gave his address as 12 Onslow Road, (Southampton). His last ship had been the St. Louis. As a third class steward he received monthly wages of £3, 15s. Reportedly, before leaving, he sent £1 to his hard-pressed family back home, the last of several.
An impressive 16' Obelisk was erected to the memory of Thomas and his Dumfriesshire shipmate John Law Hume in Dumfries. The inscription reads:
IN MEMORY OF
JOHN LAW HUME, A MEMBER OF THE BAND
AND THOMAS MULLIN, STEWARD,
NATIVES OF THESE TOWNS
WHO LOST THEIR LIVES IN THE WRECK OF
THE WHITE STAR LINER "TITANIC"
WHICH SANK IN MID-ATLANTIC
ON THE 14TH DAY OF APRIL 1912.
THEY DIED AT THE POST OF DUTY