In 1878, at the age of 20, he joined the
Irish Republican Brotherhood (IRB) following the visit to Dungannon by
John Daly, and by 1880 he was centre (head) of the local IRB circle.
Participation in Fenian dynamite campaign and 15 years imprisonment In 1883, Clarke was sent to
London, under the alias of "Henry Wilson", to take part in the
Fenian dynamite campaign advocated by
Jeremiah O'Donovan Rossa, one of the IRB leaders exiled in the United States. British authorities were already following those involved, aided by informants, and Clarke was arrested in possession of
dynamite, along with three others. He was tried and sentenced to
penal servitude for life on 28 May 1883 at London's
Old Bailey. He subsequently served 15 years in
Pentonville and other British prisons. In 1896, he was one of only five remaining Fenian prisoners in British jails and a series of public meetings in Ireland called for their release. At one meeting,
John Redmond MP, leader of the
Parnellite Irish National League, said of him: "Wilson is a man of whom no words of praise could be too high. I have learned in my many visits to
Portland for five years to love, honour and respect Henry Wilson. I have seen day after day how his brave spirit was keeping him alive ... I have seen year after year the fading away of his physical strength".
Relocating to America Following his release in 1898, Clarke returned to Ireland where he was met by a number of welcome home parties in Dublin and Dungannon, and Limerick offered him the freedom of the city, which he accepted. Clarke stayed with the family of the Mayor of Limerick at the time, the republican
John Daly, with whom Clarke had previously been imprisoned. It was during this time that Clarke was introduced to
Kathleen Daly, John's niece. Tom Clarke and Kathleen would subsequently begin a relationship. Despite his well-wishers, Clarke found it difficult to gain employment in Ireland following his return and would make the decision in 1900 to emigrate to
Brooklyn in the United States. In 1901, he married Kathleen, 21 years his junior. The Irish nationalist
John MacBride served as Clarke's best man.
Return to Ireland, political activism Reasoning that he needed to be in Ireland to continue his Fenianism, Clarke returned to Ireland in November 1907, where he opened up a
tobacconist shop in
Dublin while immersing himself back into the IRB which was undergoing a substantial rejuvenation under the guidance of younger men such as
Bulmer Hobson and
Denis McCullough. Clarke developed a very close kinship with Hobson, who along with
Seán Mac Diarmada, became his protégé. The younger, more radical members of the IRB lauded Clarke for his militancy, and with their support, Clarke was quickly promoted to the Supreme Council of the IRB and made treasurer. It was alongside Hobson and Mac Diarmada that Clarke would establish the republican journal
Irish Freedom in 1910. However, he was critical of Irish trade unions' dependence on their English counterparts and regarded the Labour movement as a minor secondary struggle when compared to that for Irish Independence. In the summer of 1913 Clarke once again organised a gathering of republicans at Bodenstown. In that year Clarke invited a young man,
Paidraig Pearse, to give the oration. By November of that year, Clarke had brought Pearse into the IRB, despite some reservations by other members of the IRB who feared that Pearse was politically unreliable and too personally ambitious. == Irish Volunteers ==