McDermottroe was born in
Sligo town in the 1950s, one of four children (including writer/director Conor) Her first theatre role was in a production of
The Merchant of Venice featuring
Micheál Mac Liammóir and
Hilton Edwards. She married John Costigan, future Executive Director of Dublin's
Gaiety Theatre, in 1979, having first met in 1977. They have two children including writer Nora Costigan and actress
Gina Costigan. They live in
Dún Laoghaire. Her character in
Glenroe was introduced in 1995, as Venetia, the matriarch of the Crosby family. Venetia later divorced and married divorcé Dick Moran. In
Pat Shortt's rural sitcom,
Killinaskully, McDermottroe portrayed
Mrs. Gilhooley, known for repeatedly not being "in the habit of repeating" herself, She played crime figure
John Gilligan's wife in 2003's
Veronica Guerin, a film in which her daughter
Gina Costigan portrayed the wife of criminal figure
John Traynor. In 2017, she played Carmel in
Isobel Mahon's
Boom?. Her film credits include
John Huston's
The Dead,
John Erman's
The Blackwater Lightship, and
The Winter Lake. She was named "Best Actress", at the 2023 Milan Gold March Awards, for her role in
The Carer. ==Filmography==