Helgenberger departed Ryan's Hope in January 1986 and was subsequently replaced in the role of Siobhan by Carrell Myers.

Helgenberger guest starred in an episode of ABC's mystery/detective series based on Robert B.

Helgenberger played the French horn in her high school (North Bend Central High School) marching band.

While performing in a summer of 1981 NU campus productions of Shakespeare's Taming of the Shrew, in which she played Kate, Marg was spotted by a scout for the TV soap opera Ryan's Hope.

Soon after completing college, Marg landed her first professional acting role on the long-running ABC Daytime soap opera, playing uptight amateur cop Siobhan Ryan Novak (1982–1986), a role previously played by Sarah Felder and Ann Gillespie.

Actually, this invitation is but a smokescreen, so that Frasier can "accidentally" run into his newest dream girl Emily (Helgenberger).

Helgenberger scored another big break when she snagged the co-starring role of Catherine Willows, a former show girl employed as a blood spatter analyst on the CBS drama CSI: Crime Scene Investigation.

Parker's Spenser novels, Spenser: For Hire, NBC's legal drama Matlock and ABC's drama thirtysomething.

She also played a regular role as Natalie Thayer, opposite Margot Kidder and James Read, on CBS’ six-episode drama comedy series Shell Game (1987). C." Koloski, a heroin-addicted prostitute on the ABC war drama series China Beach, was Marg’s first prominent role.Her performance from 1988 to 1991 on the highly-acclaimed dramatic series won an Emmy Award for Outstanding Supporting Actress in a Drama Series in 1990.Meanwhile, in 1989, Marg made her feature film debut in a leading role as an all-night answering service operator in one segment of the Wheat brothers’ horror anthology After Midnight.Additionally, she was also seen opposite Bruno Kirby in I'll Be Waiting, a segment of Showtime's Fallen Angels helmed by Tom Hanks, and as a novelist on the ABC miniseries Stephen King's The Tommyknockers opposite Jimmy Smits.She was also seen in the CBS miniseries When Love Kills: The Seduction of John Hearn and made her first collaboration with director Peter Weller in Showtime's Partners.During her stint on the hit show, Marg supported Julia Roberts in the film Erin Brockovich and portrayed Patsy Ramsey in the CBS miniseries about the mysterious murder of 6-year-old beauty pageant contestant Jon Benét Ramsey in Perfect Murder, Perfect Town.