[1] Quelch joined the Social Democratic Federation (SDF),[2] 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.
[3] 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.
[4] 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.
[5] Quelch was delegated with such as John S. Clarke, Helen Crawfurd, Williie Gallacher, William McLaine, JT Murphy, Sylvia Pankhurst,[6] Marjory Newbold Dave Ramsay and Jack Tanner to attend the Second Congress of the Comintern and attended the Baku Congress of the Peoples of the East.