His parents were Elizabeth O'Neill, daughter of Dr.O'Neill, and Timothy Charles Harrington, a Nationalist MP, barrister-at-law and Lord Mayor of Dublin from 1901 to 1903.
He attended the Christian Brothers' school in Edward Street, Tralee, and later Rockwell College in County Tipperary.
He was ordered to Dublin to deliver a dispatch and remained there on advice after a secret meeting with Cathal Brugha and Austin Stack, and later a note from Michael Collins.
After the Anglo-Irish Treaty he became a private in the Medical Corps of the Irish Army in March 1922, reprising his pharmacy practice.
His final military post was as Deputy Director of Intelligence at General Headquarters from 1952 to 1959, in the rank of lieutenant colonel.
[2] Upon retiring from his military role, Harrington was appointed National Organiser of the Federated Union of Employers [now part of Ibec], remaining until 1973.
[2] Harrington wrote and presented a number of different items on 2RN (later Radio Éireann) from the 1930s onwards, and his play, Resurgence – A Cavalcade of the Easter Insurrection, was broadcast in 1937.
[2] In the book, Harrington referred to murders on both sides in the Civil War, including the notorious incidents at Ballyseedy Cross, Countess Bridge, and Bahags, all in County Kerry, where captured Republicans were brutally killed using landmines, bombs and bullets by Free State soldiers of the Dublin Guard.