Ellen was born on November 10, 1969 in Everett, Massachusetts.
She was raised in the working-class Boston-area neighborhood by her father and five siblings (all at least eight years her senior) after her mother passed away when she was four. She later moved to New York's Upper West Side, then to Miami, where she worked as a waitress.
In 1996, she was approached by an agent about appearing in commercials, and subsequently appeared in commercials for Citibank and L'Oreal. Minor roles on TV series and forgettable films followed. Pompeo moved to Los Angeles in 2001 in an attempt to get serious about her acting career. In 2002, her big break came when she was cast in a crucial role in Moonlight Mile.
Her star grew slowly but surely thereafter, with an appearance in Daredevil as Matt Murdock's secretary, then a starring role in Old School as Nicole, the love interest of Mitch (Luke Wilson). She also appeared in Catch Me If You Can alongside Leonardo DiCaprio, and guest starred on Law & Order and an episode of Friends.
In 2005 she was set to star in a television pilot called Secret Service, in which she played the head of that organization. That show was shot down by every network, but ABC executives liked her, and her next project, a pilot called Grey's Anatomy, was picked up. The rest, as they say, is history.