O’Byrne is born on December 8, 1929, in Killiney, a suburb of Dublin, the son of John O’Byrne, KC, and Marjorie (née McGuire). He attends St. Mary’s College, Dublin, Castleknock College and University College Dublin (UCD), where he earns a degree in Legal and Political Science. In 1952, he is called to the King’s Inns. In 1954, he abandons a legal career in favour of the performing arts, joining the George Mitchell Singers in London but has a “day job” working for an insurance company. During the summer season in Llandudno, Wales, he meets and later marries a singer and dancer from Dublin named Vicky Fitzpatrick. They have three children, Jane, John, and Dominic.
O’Byrne emigrates to the Union of South Africa in 1958. In 1961, he wins a competition called The Voice of South Africa, thereby gaining a contract with the South African Broadcasting Corporation and a new career. As is commonly the case at the time, both among Irish actors abroad as well as many South Africans in the theatre and broadcast media, he uses Received Pronunciation for his professional speaking voice.
In 1980, when the radio station Talk Radio 702 is launched in Johannesburg, O’Byrne is the first announcer heard on it. He also works for Radio Today and Radio Veritas, a Roman Catholic station, in Johannesburg and for Fine Music Radio in Cape Town. He also works for the BBC on Radio 2 and Capital Radio in the United Kingdom, during the 1970s and 1980s.
O’Byrne is also an actor, and narrates five films, while in South Africa. He is one of a series of actors who play the science-fiction character Mark Saxon in the original radio drama No Place to Hide, originally created by South African author Monty Doyle.
O’Byrne and his family move to Mullingar in 2001, but he continues to do broadcasts for Irish classical-music radio station RTÉ lyric fm, and his programmes for Fine Music Radio are recorded there and transmitted to South Africa for broadcast. He retires in 2004.
In 2010, at the MTN Radio Awards Gala, in Johannesburg, O’Byrne is honoured for his contribution to South African broadcasting, being named one of the inaugural inductees into the Radio Hall of Fame.
O’Byrne dies in Mullingar at the age of 83 on December 4, 2013.