At age of twelve, O'Siadhail attended the Jesuit boarding school Clongowes Wood College, an experience he later described in some of his poetry.
[3] Micheal O'Siadhail studied at Trinity College Dublin (1964–68) where his teachers included David H. Greene and Máirtín Ó Cadhain.
For seventeen years, O'Siadhail worked as an academic; firstly, as a lecturer at Trinity College (1969–73), where he was awarded an MLitt in 1971, and then as a research professor at the Dublin Institute for Advanced Studies.
In 2018, O'Siadhail was included in The Tablet magazine's ′Fifty Minds That Matter′ – fifty men and women who are ″adding some Catholic salt to the contemporary cultural soup″.
In 1978, O'Siadhail published his first poetry collection The Leap Year (originally written in Irish), which was a meditation on healing and nature set against an urban background.
There were two more collections which contained a few of his best-known poems, Springnight in 1983 and The Image Wheel in 1985, before he went full-time and began a series of books based on broad themes.
It evokes the Holocaust from its origins to its aftermath in a book-length sequence of stark intensity and was shortlisted for the Jewish Quarterly-Wingate Literary Prize.