Thomas's father Hugh Sydney Marsham-Townshend of Scadbury Park, Chislehurst had two sons: John, with his first wife Cicely Bunbury, and Thomas, with his second wife Laura Constance Elinor Bunbury (Cicely’s sister).

Thomas was educated at Eton where he was in the Junior Division of the OTC and Matriculated in 1934. He was up for only one year.

In March 1936, he was gazetted to the Scots Guards. In October 1937, he was gazetted as a Second Lieutenant on probation on the Supplementary Reserve of Officers. He was promoted to Captain on 17 August 1942.

He married Averil Innes Loyd on 22 January Cairo. Their first daughter was born in the Hotel Cecil in Alexandria on 30 June 1942.

Thomas died of wounds in Italy on 24 January 1944.

Thomas died of wounds received at Monte Cassino.

He was first buried at Carinola and later at Minturno War Cemetery Plot I, H, 24.

His second daughter Susan was born on 13 May 1944 at 16 Sharia El Nabatat, Garden City Cairo.

By the end of October 1943, the Allies were facing the German winter defensive position known as the Gustav Line, which stretched from the River Garigliano in the west to the Sangro in the east. Initial attempts to breach the western end of the line were unsuccessful and it was not until 17 January 1944 that the Garigliano was crossed, and Minturno was taken two days later. The site for the cemetery was chosen in January 1944, but the Allies then lost some ground and the site came under German small-arms fire. The cemetery could not be used again until May 1944 when the Allies launched their final advance on Rome. The burials are mainly those of the heavy casualties incurred in crossing the Garigliano in January.

He is commemorated by a wooden cross in the Scadbury Chapel at St Nicholas Church, Chislehurst.

The Townshend family were connected with Scadbury Park from the 1750s. Thomas’s two daughters inherited the estate in 1975. In 1983, it was bought by the London Borough of Bromley and is now managed as a farm and local nature reserve.