Maria Bello was born in Norristown, Pennsylvania, the daughter of Kathy, a teacher and school nurse, and Joe Bello, a contractor. Her father is Italian American and her mother Polish American. She grew up in a working-class Roman Catholic family and graduated from Archbishop Carroll High School (Radnor, Pennsylvania). Later she attended Villanova University, majoring in political science. She intended to become a lawyer, but took an acting class during her senior year, just for fun. She was soon cast in small off-Broadway plays, such as The Killer Inside Me, Small Town Gals With Big Problems and Urban Planning. She later guest-starred on episodes of The Commish (1991), Nowhere Man (1995), Misery Loves Company (1995) and Due South (1994).

Bello's breakthrough came when producers Kerry Lenhart and John J. Sakmar cast her as Mrs. Smith in the spy show Mr. & Mrs. Smith. The show was cancelled after just eight weeks on the air. Then came a guest stint on ER as the feisty pediatrician Dr. Anna Del Amico, in which she guest-starred in the final four episodes of the third season. Bello remained on the show for one season, departing after the medical drama's 4th season. The actress went on into movies landing a role in Coyote Ugly. She has been nominated for the Golden Globe award twice: for Best Supporting Actress in The Cooler (2003) and for Best Actress in A History of Violence (2005).

Bello has a son named Jackson Blue, born in 2001, with former long-time boyfriend Dan McDermott. Bello is also a Muay Thai practitioner. In July 2008 she became engaged to musician Bryn Mooser.