Byrne, whose birth name is Mary Martha Byrne, began her acting career on Broadway in the hit musical Annie, in which she played the role of July and also understudied the title role. On television, Byrne starred in When the Cradle Falls, a CBS movie-of-the-week. She appeared in numerous primetime series including Murder, She Wrote; Kate and Allie; Jake and the Fatman; In the Heat of the Night; Doogie Howser, M.D.; The Young Riders; Parker Lewis; Over My Dead Body; Pros and Cons, with James Earl Jones; and Hearts are Wild, as Lainie Kazan's daughter. She starred in the 1983 summer series The Hamptons and appeared in the television films Pink Lightning; Drop-Out Father, with Dick Van Dyke and Mariette Hartley; She's Hired, He's Fired, with Wayne Rogers and Karen Valentine; The Harvest on PBS; HBO's Anna to the Infinite Power, in which she played the title role; and the Disney Channel's The Eyes of the Amaryllis. She also lists working with Bob Hope on one of his specials as a highlight in her career.

Byrne has also released three CDs, Martha Byrne, which includes songs that she has performed on As The World Turns; Woman Thing Music; and most recently, The Other Side. In addition, she just produced the soundtrack to the Calista Flockhart film Jane Doe.

Since 1996, Byrne has hosted the annual Daytime Television Salutes St. Jude Children's Research Hospital benefit, where daytime stars from ABC, NBC, and CBS meet and greet fans and treat them to live musical performances. Daytime devotees have the opportunity to mingle with the stars, as well as bid on over 100 auction items, with all profits going toward the hospital.

Martha currently lives in New Jersey with her husband, Michael McMahon, and sons, Michael (born May 29, 1998) and Maxwell (born Sep 3, 2002), and daughter, Annmarie.

June 17, 2009 to September 10, 2009

The Bold and the Beautiful
Herself/scriptwriter
April 2009 to Present

As The World Turns
Rose D'Angelo
April 2000 to December 12, 2003

When the Cradle Falls
Donna
1997

Silk Stalkings
December 12, 1991

Pink Lightning
Jill
1991

Drop-Out Father
Elizabeth McCall
1982

The Hamptons
1983

HBO's Anna to the Infinite Power
Anna
1983

Disney Channel's The Eyes of the Amaryllis
1983

She's Hired, He's Fired
1984

As The World Turns
Lily Walsh Mason Snyder Grimaldi Snyder
April 1985 to October 1989; April 1993 to April 22, 2008