Thomas was born in 1910 in Folkestone, where he grew up to attend the Harvey Grammar School. Upon leaving he joined the Royal Navy.

HM Submarine Upholder was launched in May 1940 and following its commissioning five months later, sailed for Malta under the command of Lieutenant Commander Wanklyn with orders to join the 10th. Submarine Flotilla. Able Seaman Thomas Brown joined the crew at this time.

The Mediterranean was a dangerous area for submarines to operate, owing to its shallow and clear waters. By the time Upholder arrived in Malta, not only had nine other submarines been lost but the enemy had begun the second siege of the island. Food was strictly rationed, torpedoes in short supply and the submarines spent many daylight hours submerged at their berths to avoid detection from Axis aircraft.

Nevertheless the 10th Flotilla carried out patrols and attacks on convoys that sailed from Italy to supply the Afrika Korps in Libya. Upholder was the most successful of the Malta-based submarines as well as becoming the most successful British submarine in World War 2.

In sixteen months of continuous action they completed 24 patrols, sinking twenty ships, including a destroyer, two Italian submarines and a minesweeper. She also accounted for three troopships, thus making a significant contribution towards disrupting the supply and reinforcement of Rommel's desert forces.

The crew were exhausted but nevertheless sailed on their twenty fifth patrol. They had been ordered to a patrol line off the Libyan coast along with two other vessels from the 10th. Submarine Flotilla. They never returned. It is possible that the Upholder was spotted by an enemy reconnaissance aircraft which enabled the Italian torpedo boat Pegaso to sink her with depth charges.

There were no survivors.