Born on Feb. 8, 1969 in Plainfield, NJ, McCormack was raised the second of three children by her father, William, a former car dealership and ice cream parlor owner, and her mother, Norah, a clinical therapist. McCormack had her first taste of performing on stage when she was 12 after appearing in a production of the Christmas opera, “Amahl and the Night Visitors” (1981). After performing in local productions and graduating from the Wardlaw-Hartridge School in 1987, she attended Trinity College in Hartford, CT, where she majored in English and continued appearing on stage in plays and musicals. Once she left Trinity in 1991, McCormack moved to New York City, where she appeared in off-Broadway productions at the Atlantic Theatre Company and Naked Angels, while honing her craft at the William Esper Studios. A few short years later, McCormack made her television debut with a guest-starring turn on “Law & Order” (NBC, 1990- ) – practically a rite of passage for any up-and-coming New York actor – which she followed with her feature film debut in John Hughes’ forgettable remake of “Miracle on 34th Street” (1994), starring Sir Richard Attenborough as Kriss Kringle.
With her career rapidly taking off, McCormack began working onscreen with more regularity. After an episode of the short-lived drama series “The Wright Verdicts” (CBS, 1995), she had a role opposite an aged Robert Mitchum in “Back Fire!” (1995) – an awful spoof of Ron Howard’s ode to firemen, “Backdraft” (1991). McCormack had her first significant breakthrough with a regular series role on the drama “Murder One” (ABC, 1995-97), playing a high-minded and devoted associate attorney working for a dogged and brilliant criminal attorney (Daniel Benzali). The show was canceled after two seasons, leaving McCormack to return to working predominantly in features for the next several years. She gained considerable notice for her prominent co-starring role in the film of radio personality Howard Stern's memoir, "Private Parts" (1997). Given Stern's reputation, McCormack initially opted to pass on the part of his long-suffering wife Alison, but was talked into reading the script by her agent. Excited by the dimensionality of the character, as well as the overriding love story theme of the script, she took on the role and delivered a humorously memorable portrayal of Mrs. Stern, which not only changed minds about the self-proclaimed King of All Media, but also exposed the actress to a much wider audience.
Continuing her career uptick, McCormack had strong supporting roles as Stanley Tucci’s scheming assistant in the screwball comedy “The Alarmist” (1998), which she followed with a smaller part as a pilot in the blockbuster disaster flick, “Deep Impact” (1998). Keeping a busy schedule, she was an infertile woman married to a religious fanatic in "Getting to Know You" (1999) which debuted at Sundance, before playing a DEA agent in "Harvest" (1999), a drama about farmers growing marijuana to financially preserve their land. McCormack was also featured as a romantic partner for director-star Clint Eastwood in the thriller "True Crime" (1999), as well as portrayed the wife of a small-time hockey player (Russell Crowe) who ends up in a game versus the New York Rangers in "Mystery, Alaska" (1999). Rounding out a hectic year, she scored a supporting role in "The Big Tease" (1999), a comedy about a small town Scottish hairdresser (Craig Ferguson) who enters the hairdressing world championships in Los Angeles.
In addition to her numerous film appearances, theatergoers saw McCormack return to the stage in a high-profile role that utilized her capable singing voice, succeeding luminaries Natasha Richardson and Jennifer Jason Leigh as Sally Bowles in the popular Broadway revival of "Cabaret" (1999). Meanwhile, she had supporting turns in "The Broken Hearts Club: A Romantic Comedy" and "Gun Shy" (2000), an Eric Blakeney action comedy starring Liam Neeson and Sandra Bullock. She also starred alongside Minnie Driver in the woeful crime comedy "High Heels and Low Lifes" (2001), playing a struggling actress who gets caught up in a blackmail scheme with her best friend (Driver). The actress fared better in writer-director Bart Freundlich's ensemble drama "World Traveler" (2001), which she followed with a fine, but underutilized turn as Jeff Bridges' wife in the dramedy "K-PAX" (2001). McCormack was particularly excellent as the depressed, lovelorn masseuse in "Full Frontal" (2002), director Steven Soderbergh's artsy, low-tech and chilly meditation on Los Angelinos. She next detoured to play the adoptive mother of David Spade's full-grown ex-child actor in "Dickie Roberts: Former Child Star" (2003).
Back on television, which soon proved to be her bread-and-butter medium, McCormack starred on “K-Street” (HBO, 2003), a partially-improvised drama centered inside the realm of politics and political advisors at a fictional lobbying firm headed by real-life consultants James Carville and Mary Matalin. Following a two-episode arc on “ER” (1994-2009) and a starring role in the three-parter “Traffic: The Miniseries” (USA Network, 2004), she began a two-year stint on “The West Wing” (NBC, 1999-2006), playing Katherine Harper, the Deputy National Security Advisor to President Josiah Bartlet (Martin Sheen). Once “The West Wing” wound down, McCormack starred in the independent drama “Madison” (2005) and was cast as a pilgrim woman in the Hollywood satire “For Your Consideration” (2006). After co-starring opposite John Cusack and Samuel L. Jackson in the supernatural horror flick “1408” (2007), McCormack appeared as federal marshal Mary Shannon on an episode of “Law & Order: Criminal Intent” (NBC, 2001- ), which was really an introduction for her own series, “In Plain Sight” (USA Network, 2008- ), a comedic drama that focused on Shannon overseeing a community of people in the Witness Protection Program, while trying to maintain some semblance of a personal life. Meanwhile, she earned a Tony Award nomination for her Broadway performance in “Boeing-Boeing” (2008).