Born in the Pentonville Road area of London, Cantwell spent some time working as a basket-maker before entering the printing trade.
[2] The anarchist wing of the league became increasingly prominent, and from 1890, all the key posts were held by anarcho-communists.
The following year, he was arrested for putting up posters calling for a protest against the wedding of Prince George, Duke of York, and Princess Mary of Teck, which stated that "He who would be free himself must strike the blow".
Cantwell denied advocating violence, but was found guilty and served six months in prison.
He worked as a compositor for anarchist publications, but suffered a stroke in 1902, and thereafter was in poor health, dying in 1906.