After returning to Dublin in the early 1980s, McEvoy got a job as a runner at the Dublin Theatre Festival and studied acting at the Oscar Theatre School. McEvoys earlier theatre work includes
The Philanderer (
George Bernard Shaw) and
Semi-Private (
Mary Halpin) at The Gate. She starred with
Siobhán McKenna in the original production of
Bailegangaire (
Tom Murphy) and
Wood of the Whispering (
M. J. Molloy) with
Druid Theatre directed by
Garry Hynes, also Charlie's Aunt at the
Gaiety Theatre, Dublin. While at Oscar Theatre School she auditioned for Biddy Byrne in
Glenroe and was given the part because she had a licence to drive tractors. From 1983 through to 2000, Byrne became one of Ireland's best known television actresses in her role as Biddy McDermott in
Glenroe. Mary left the show in 2000 saying "I was out shoveling in the goose pen in
Glenroe and I just said, "I can't do this anymore. It wasn't that I didn't like it; it was just I knew that I had to jump and if I didn't do it now I'd be wondering, 'what if' for the rest of my life."" After this Mary told the producers she wanted to leave the soap and her character Biddy was killed off in a car crash in May 2000, leaving fans of the show shocked. A few weeks later her co-star Joe Lynch announced he was also leaving the show.
Glenroe was axed a year later in 2001. McEvoy has appeared in the following films:
How to Cheat in the Leaving Certificate,
Moll Flanders and
The Pear Bottle. After leaving
Glenroe, McEvoy has featured in the plays
Big Maggie,
Sive,
The Field,
The Chastitute,
The Vagina Monologues,
Shirley Valentine,
The Matchmaker,
The Year of the Hiker,
Dancing at Lughnasa,
Whippy,
The Life and Times of Selma Mae,
Moonlight and Music and
Jo Bangles. In 2010, McEvoy became a regular guest panelist on the
TV3 show
Midday and also was a guest on
The Late Late Show in April 2011. In April 2011, McEvoy released her autobiography
How The Light Gets In. ==Personal life==