David Andrew Thornley, Irish Labour Party politician and university professor at Trinity College Dublin, is born in Surrey, England, on July 31, 1935.

Thornley is the youngest child of Welshman Frederick Edward Thornley and Dublin-born Maud Helen Thornley (née Browne). His parents, both civil servants, meet while working in Inland Revenue in Dublin in the 1910s.

Thornley receives a BA and PhD at Trinity College Dublin. His PhD is entitled “Isaac Butt and the creation of an Irish Parliamentary Party (1868–1879)” and is written under the supervision of Theodore William Moody. Working as a presenter on 7 Days since 1963, he is appointed Associate professor of Trinity in 1968. In 1964, he publishes the book Isaac Butt and Home Rule.

After joining Labour in 1969, Thornley is elected to Dáil Éireann as a Labour Party Teachta Dála (TD) for the Dublin North-West constituency at the 1969 Irish general election. He confronts the party leader Brendan Corish, who at the time of the Arms Crisis reportedly rejects out of hand any suggestion of military aid or use of force after the outbreak of violence in Northern Ireland.

Thornley considers himself to be “in the mould of James Connolly,” being a practising Catholic, Marxist and republican.

In December 1972, Thornley calls for the immediate release of Seán Mac Stíofáin, then leader of the Provisional Irish Republican Army. He is re-elected at the 1973 Irish general election. In April 1976, he loses the Labour Party whip after appearing on a Sinn Féin platform during Easter Rising commemorations. In September 1976, he votes for the Criminal Justice (Jurisdiction) Bill despite misgivings. He tells The Irish Times, “When I get very depressed, I drink too much. When I voted for the Criminal Justice (Jurisdiction Bill) I went on the batter for a forthnight [sic].” In February 1977, he is re-admitted to the Labour Parliamentary Party. He loses his seat at the 1977 Irish general election.

In 1978, Thornley joins the newly formed Socialist Labour Party (SLP) stating that he has done so because “There is no man in politics that I respect more than Noël Browne, despite our occasional differences. If the SLP is good for him, it’s good enough for me.”

Overweight, afflicted with undiagnosed diabetes, his judgement increasingly erratic, from the early 1970s Thornley suffers a steady deterioration of health, compounded by his heavy drinking, on which he relies to cope with stress and emotional depression. On one occasion he collapses in the Dáil and is attended by party colleague Dr. John O’Connell. He dies at the age of 42 on June 18, 1978, one week after admission into Jervis Street private nursing home. After a sung Latin Requiem Mass in St. Andrew’s Church, Westland Row, Dublin, he is buried in Bohernabreena Cemetery, County Dublin.

The Trinity College Labour Branch is formerly named the David Thornley Branch in his honour.