She was born in Philadelphia on November 5, 1963. While studying dance as a child, she was spotted by a talent agent who got her work in a number of television commercials, which lead to her two-and-a-half year stint on the soap opera Search for Tomorrow.

McArdle's big break came in early 1977 when she was pulled from the chorus to replace the star in the Broadway musical Annie during rehearsals. The show was a critical and commercial smash, and she became the youngest performer ever to be nominated for a Tony Award as Best Lead Actress in a Musical. She lost to co-star Dorothy Loudon--who played Miss Hannigan--but did receive the Theater World and Outer Critics' Circle Awards for her performance. In April 1978, she opened in London's West End production.

Her first assignment after returning to the States was the plum role of Judy Garland in NBC's telepic Rainbow, but throughout her career she has concentrated primarily on performing in musical theater and cabarets. Her credits include Les Misérables (both on Broadway and in the national tour), Jerry's Girls (a revue of Jerry Herman songs co-starring Carol Channing and Leslie Uggams) Beauty and the Beast, Starlight Express, Meet Me In St. Louis, They're Playing Our Song, and another celebrated Annie in Irving Berlin's classic, Annie Get Your Gun. She briefly appeared in the 1999 Rob Marshall-directed TV version of "Annie," singing a segment of the song "N.Y.C."

McArdle has performed in the showrooms of many of the casino hotels in Las Vegas and Atlantic City, and in cabarets such as Odette's in New Hope, Pennsylvania and the King Cole Room at the St. Regis Hotel and Freddy's Supper Club in Manhattan.