Thomas was the son of John Maynard Roskilly and Frances Mary Abel. He was born in 1922 in Tavistock where both families had been farmers for generations. He had an older sister and a younger brother.

He was educated at Tavistock Grammar School and Matriculated in 1939. He graduated with a 3rd in Classical Mods in 1941.  He joined the RAF.

At around 20.00 on 10 January 1946 de Havilland Mosquito N.F. Mk.XXX NT544 of 54 OTU exploded and crashed near Keld in Swaledale in North Yorkshire. It was on a training flight from RAF Leeming.

The aircraft appeared to have flown straight into the fell at cruising speed and was largely destroyed by the impact and the ensuing fierce fire. As an RAF investigation team found no evidence of mechanical failure and icing wasn't considered to be a factor, the accident was attributed to the crew having failed to maintain a minimum clearance altitude of 2000 ft AGL as they had been briefed.

Thomas who was noted as being a very experienced airman was flying the plane. His navigator was Flight Sergeant Sidney Arthur Whiting. Both of them were killed instantly, in the crash. Witnesses said that they sustained few visible injuries, leading to local speculation as to the cause of the accident and whether they may have attempted to bail out.

He is buried in Harrogate [Stonefall] Cemetery Sec. G. Row K. Grave 1.

His mother wrote to the College after his death.

In 1945, he received a King's Commendation for Valuable Service in the Air.