John Smith Clarke, the thirteenth of fourteen children, was born in Scotland in 1885. His father worked in a circus and Clarke spent much of his early life living in gypsy encampments. After receiving little schooling he joined the circus as a horse bareback rider. At the age of seventeen he was working as a lion tamer. According to Gordon Munro: "He received the first of many injuries a few days later when a hurt lion attacked him when he entered the cage to help it."
In 1902 several political activists left the Social Democratic Federation (SDF), an organization led by H.L. Hyndman, to form the Glasgow Socialist Society. Eventually, most of the members of the SDF in Scotland joined this new group. In August 1903 it was renamed the Socialist Labour Party (SLP). The organization that had been inspired by the writings of Daniel De Leon, the man who helped establish the International Workers of the World (IWW) and the Socialist Labor Party in the United States. Clarke, who had been converted to socialism, joined the SLP. Leaders of the group included Willie Paul, Jack Murphy, Arthur McManus, Neil MacLean, James Connally, John MacLean and Tom Bell.
Clarke eventually became joint editor of the SLP journal, The Socialist, with Willie Paul, Tom Bell and Arthur McManus. In 1906 he began to organize the transport of weapons to revolutionary socialists in Russia. The operation lasted until the discovery of a cache at Blyth in Northumberland.
In 1910 Clarke moved to Edinburgh where he became editor of The Reform Journal. He also worked as a private secretary of the author Jane Clapperton (1832-1914).
John Clarke was opposed to Britain's involvement in the First World War. The historian, Nicola Rippon, has argued that "Clarke was not a pacifist, believing that the only armed struggle should be between the world's working classes and their capitalist employers."
In February 1916 the Clyde Workers' Committee became involved in a dispute at Beardmores Munitions Works in Parkhead. The government claimed that the strike was a ploy by the CWC to prevent the manufacture of munitions and therefore to harm the war effort. On 25th March, Arthur McManus, David Kirkwood, Willie Gallacher and other members of the CWC were arrested by the authorities under the Defence of the Realm Act. Sir Frederick Smith was the prosecutor. Tom Bell argued that: "It is doubtful if a more spiteful, hateful enemy of the workers ever existed... he threatened to send them to the front to be shot." The men were eventually court-martialled and sentenced to be deported from Glasgow to Edinburgh. The men lived with John Clarke until they could find other accommodation.
Over 3,000,000 men volunteered to serve in the British Armed Forces during the first two years of the war. Due to heavy losses at the Western Front the government decided to introduce conscription (compulsory enrollment) by passing the Military Service Act. The