Mason was born in New Orleans, Louisiana, and grew up in St. Louis and Chicago. She majored in theater at the University of Illinois at Chicago Circle, graduating in 1999. Mason started as a "singing hostess at Lawrence of Oregano in Chicago" in 1976 after leaving college, where she met the late pianist and composer Brian Lasser, with whom she worked until his death in 1992. Mason has performed in cabaret and with symphonies for many years. She was one of the featured cabaret vocalists at Duplex Cabaret Theatre, New York City, in the early 1980s, and in 2005 presented a program "Better Days" with songs by her late musical director Brian Lasser. She has appeared at the Bay Area Cabaret, Empire Ballroom, San Francisco in 2010. She continues to perform her cabaret act at such venues as Davenport's in Chicago in 2011 and The Iridium in 2011. She taught at the Theatre Arts Center's Summer Workshops & Camp in Bayside, Queens, New York in 2010. She first appeared on Broadway in Play Me a Country Song in 1982. She took the role of standby to Glenn Close as Norma Desmond in Sunset Boulevard in the Los Angeles production in 1993, and went on to play almost 300 performances over two years both in Los Angeles and on Broadway. She originated the role of Tanya in Mamma Mia!, playing the role from October 5, 2001 to October 6, 2002. She took over the role of Velma Von Tussle in Hairspray on April 6, 2008. She was the Queen of Hearts in Wonderland in 2011 on Broadway and in the Tampa and Houston productions in 2009–2010. Mason appears in the US tour of A Christmas Story, The Musical! starting in November 2011. In 2011, Mason was scheduled to play Mrs. Danvers in the musical Rebecca on Broadway. In 2017, Mason used a song to call for marriage equality. Mason appeared on tour in Andrew Lloyd Webber's Love Never Dies as Madame Giry. The tour ended on December 2, 2018.
Work
Broadway
Play Me a Country Song
Jerome Robbins' Broadway
Sunset Boulevard
Mamma Mia!
Hairspray
Wonderland
Off Broadway
Karen Mason Sings Broadway, Beatles, and Brian, 1986, Minetta Lane Theater
Recording' Mason has recorded 6 solo albums, including Right Here, Right Now. She appears on the cast recordings of And the World Goes 'Round and Wonderland''.
Personal life
Mason is married to Paul Rolnick, a producer and composer.
Awards
Mason has received 10 MAC Awards, including the 2004 MAC Award for Major Female Vocalist, and three Bistro Awards.