Born in County Meath in 1629, he studied for the priesthood in Rome and was ordained there in 1654. After some years of teaching and service to the poor of Rome he was appointed Archbishop of Armagh in Ireland. Four years later, in 1673, a new wave of anti-Catholic persecution began, forcing Archbishop Plunkett to do his pastoral work in secrecy and disguise and to live in hiding. Meanwhile, many of his priests were sent into exile; schools were closed; Church services had to be held in secret and convents and seminaries were suppressed. As archbishop, he was viewed as ultimately responsible for any rebellion or political activity among his parishioners.

Archbishop Plunkett was arrested and imprisoned in Dublin Castle in 1679, but his trial was moved to London. After deliberating for 15 minutes, a jury found him guilty of fomenting revolt. He was hanged, drawn and quartered in July 1681.

Pope Paul VI canonized Oliver Plunkett in 1975.