Mary Martha Byrne (born December 23, 1969 in Ridgewood, New Jersey) is an American actress.

Byrne began acting at a young age when she joined the cast of the Broadway musical Annie, where she played the role of July.

She was a featured actor on a number of prime time episodic television programs, including Kate and Allie, Murder, She Wrote, Parker Lewis Can't Lose, Jake and the Fatman, and Hearts are Wild. Byrne also appeared in several television movies, with featured roles in When the Cradle Falls, Pink Lightning, and the HBO movie Anna to the Infinite Power, where she played the title role.

Byrne is best known for her role on the soap opera As the World Turns, as Lily Walsh Snyder. She initially assumed the role from Lucy Deakins in May 1985 and played Lily until October 1989, when she left the show and Heather Rattray assumed the role of Lily. Byrne returned in April 1993.

Byrne became part of a "supercouple" when then-head writer Douglas Marland paired Lily, a "poor little rich girl", with hard-luck farmhand Holden Snyder, played by Jon Hensley. The couple is still popular today.

In 1987, Byrne was involved in controversy when she taped Lily's first love scene months before her own 18th birthday. Lily lost her virginity to the character of Dusty Donovan; to add to the controversy, actor Brian Bloom, who was playing Dusty, was even younger than Byrne.

This provoked controversy (as teenage characters are generally portrayed by actors who are a few years older, and therefore of consenting age).

From 2000 until 2003, Martha Byrne assumed a double role when she played Lily's long-lost twin, Rose D'Angelo.

Byrne is also a singer, having released her self-titled album, Martha Byrne, in 1996.

She has also released a second album, Woman Thing Music. Byrne again was the subject of controversy, as the sponsor of the second album was Philip Morris. The CD could only be purchased in conjunction with the purchase of cigarettes, or at one of the "Woman Music Thing" concerts that Philip Morris sponsored. Byrne eventually withdrew endorsement from the music label, as she did not want to be associated with a product that could encourage underage smoking.

In 2006, Byrne realized another album entitled, "The Other Side."

Byrne is an eight-time Daytime Emmy Award-nominee, winning Outstanding Younger Actress in 1987 and Outstanding Lead Actress in 2001.