A civil servant and an evening student at University College Dublin, Clarke joined the Irish Republican Army and was captured after the Ireland Republican Army raided a British Army barracks in Omagh, County Tyrone. He was sentenced to ten years" imprisonment. In the 1955 United Kingdom General Election, Clarke was elected Member of Parliament for the Fermanagh and South Tyrone constituency, winning 30,529 votes, and becoming the youngest Member of Parliament at the time.
The case appeared before the Northern Ireland High Court in August 1955.
On 2 September, the court ruled that Clarke was ineligible for election and his Unionist opponent was declared duly elected. He petitioned for remission of his sentence in 1958, and was released from jail on 18 December 1958 after the Governor of Northern Ireland Lord Wakehurst exercised his prerogative of mercy.
41st United Kingdom Parliament]
When the House of Commons Library updated its list of previous Members of Parliament in 2010, Clarke was listed as having died, although the date of his death was not recorded.