Mary Catherine McCormack (born February 8, 1969) is an American actress. McCormack began her acting career at age 12 performing in Gian Carlo Menotti's Christmas opera, Amahl and the Night Visitors. She continued her stage work in many more musicals, and finished an acting program at the William Esper Studio. She has worked in many New York theater productions, including The Atlantic Theater Company, Alice's 4th Floor and Naked Angels, where she appeared in Jon Robin Baitz's A Fair Country.
McCormack is appearing in a new television series for the USA Network, In Plain Sight. Her previous television roles include Justine Appleton on Murder One (1995–1997); and Kate Harper on The West Wing (2004–2006). She also starred in the HBO series K Street, which aired for only ten episodes.
McCormack was nominated for the 2008 Tony Award for Best Performance by a Featured Actress in a Play for the role of Gretchen in the 2008 Broadway revival of Boeing Boeing.