Thomas Quelch (1886 – 1954) was the son of veteran Marxist Harry Quelch and a member of the British Socialist Party in the early part of the 20th century, becoming a communist activist in Great Britain in the 1920s.
Quelch joined the Social Democratic Federation (SDF), of which both his father, Harry, and his uncle, Lorenzo were members. The SDF formed the British Socialist Party (BSP), and Quelch came to attention in 1912 when he issued an appeal for soldiers to refuse to act as strikebreakers. This caused a Conservative MP, Oliver Locker-Lampson, to complain about him in the House of Commons. Quelch was involved in founding The Call in 1916, resisting attempts to turn the BSP into a Social Patriotic organisation at the outbreak of the First World War. However he was reluctant concerning the presence of African workers in the United Kingdom, raising concerns not merely that they might scab on strikes, but also that they might strike up sexual relationships with English women.
He was one of 13 conveners of the Leeds convention to hail the Russian Revolution, held on 3 June 1917, and was appointed a member of the Central Committee of the Council of Workers' and Soldiers' Delegates at the event.
Quelch was delegated to attend the Second Congress of the Comintern and attended the Baku Congress of the Peoples of the East. He was elected to the Executive Committee of the Communist International, and also served on the Central Committee of the Communist Party of Great Britain (CPGB) from 1923 until 1925.