She grew up in a Catholic family, with her parents Francis and Julia (née McGonagle) O'Donnell, and her siblings: John (the eldest), Kathleen, James; and the youngest Daniel, who is also a singer.

In the next five decades, Margo sold over 1 million records,[citation needed] and performed with Johnny Cash, Loretta Lynn and Dolly Parton.

[citation needed] Her 2019 album "Old and New" contains original tribute songs to two of her greatest influences, Liz Anderson and Jean Shepard.

Margo was named "2007 Donegal Person Of The Year" and spent most of 2007 travelling Ireland acting as an ambassador to the county.

[citation needed] Since 1977, she has been active in the search for Mary Boyle, a distant relative from Kincasslagh, who went missing at age six near Ballyshannon, County Donegal.