Julianna was born in Spring Valley, New York (just outside New York City), on June 8, 1966. She is the youngest of three daughters. Her father, Paul, is an advertising writer, and her mother, Francesca, is a former dancer with the American Ballet Theater. They divorced when Julianna was still a child.
Shortly after she was born, Margulies and her family lived in Paris for two years before relocating to England. When she was five they returned to Spring Valley, where Julianna attended Green Meadow School. Five years later they moved back to England. At age 14, Margulies began high school in New Hampshire. She later attended Sarah Lawrence College. She majored in art history, spent her junior year abroad in Florence, Italy, and appeared in several plays before graduating with a B.A. in liberal arts.
While looking for acting jobs in New York, Margulies waited tables for a year until winning a role as a prostitute looking to go straight in Out for Justice
. Eventually, she supported herself by appearing in regional theater productions, at the Yale Repertory Theatre and the Asolo Theatre in Florida, as well as in national TV commercials. She guest-starred in a 1993 episode of NBC's Law & Order
and then filmed Philly Heat
, a pilot from Tom Fontana. Fontana later cast her in small recurring role as a waitress and violinist in his NBC series Homicide: Life on the Street
. In 1994 she landed the role of nurse Carol Hathaway on NBC's medical drama ER
. She left the series after six seasons.
Many roles have followed, including critically acclaimed performances in The Mists of Avalon
(2001) and The Grid
(2004), both made-for-TV productions, and a memorable recurring role as Julianna Skiff during the 2006 season of the HBO series The Sopranos
. On the big screen she has opted for more obscure roles in many independent films, though in 2006 she portrayed flight attendant Claire Miller opposite Samuel L. Jackson
in the much-hyped Snakes on a Plane