Forgoing acting lessons for actual performance experience, Cannavale became involved with Manhattan's prestigious Circle Repertory Theater. He served as a "reader" for several plays and was eventually cast as Mark Linn-Baker's understudy in Georges Feydeau's French farce A Flea in Her Ear. Cannavale soon ended up replacing Baker for two weeks. His first-rate performance secured him a role in the company's next play, Paul Rudnick's The Most Fabulous Story Ever Told.

Television powerhouse John Wells attended one of the shows and cast Cannavale in his television series Trinity. Cannavale's character, a tugboat operator, was supposed to appear in only three episodes of the show, but starred in nine. Trinity was canceled in 1998, but Wells immediately secured Cannavale for his next television venture, 1999's Third Watch. As dedicated and lovesick paramedic Robert "Bobby" Caffey, Cannavale struck a cord with female audiences.

The show was renewed for a second season, but Cannavale felt that Caffey's character was not being developed. He asked Wells to let him exit the series and to make sure he exited "big." The producer obliged his friend: Caffey left the show mid-season after being fatally shot in the chest. The dramatic two-part episode even included a "beyond the grave" meeting between Caffey and his deceased dead-beat dad. In 2001, Cannavale joined the cast of his father-in-law, Sidney Lumet's heralded television courtroom drama, 100 Centre Street. Cannavale's brazen, ambitious prosecutor, J.J. Jellinek, is a far cry from the softhearted paramedic he portrayed on Third Watch.

Debuting on the show at the beginning of its second season, Jellinek shook up 100 Centre Street -- immediately romancing a fellow lawyer and shamelessly advancing his career in any way possible. Cannavale's television career has not kept him away from theater or film. He appeared on-stage throughout the '90s, participating in productions such as Lanford Wilson's Virgil Is Still the Frog Boy and Noel Coward's In Two Keys. His movie credits include Herbe Gardner's I'm Not Rappaport (1996) with Walter Mathau and Ossie Davis, Lumet's Night Falls on Manhattan (1997), and Gloria (1999), John Irvin's HBO original film When Trumpet's Fade (1998), Phillip Noyce's The Bone Collector (1999) with Angelina Jolie and Denzel Washington, Spike Lee's 3 A.M. (2001) with Danny Glover, Alec Baldwin's The Devil and Daniel Webster (2002), and Daisy Von Scherler Mayer's The Guru (2002). Cast as friendly and outgoing lunch truck vender Joe in the critically acclaimed 2003 indie hit The Station Agent, Cannavale provided the perfect contrast to Peter Dinklage's introverted protagonist. WIth subsequent small screen roles in Kingpin and OZ that same year, the up and coming actor would become a familiar face to television viewers before once again returning to the silver screen for supporting roles in Shall We Dance?, Haven, and Romance and Cigarettes.

A recurring, Emmy-winning role on Will and Grace ensured Cannavale's continued presence on the small screen right through to the final episode of the series aired in May of 2006, with a slew of supporting performance in such the features The Night Listener, Fast Food Nation, Snakes on a Plane, 10 Items or Less, and Dedication that same year proving that Cannivale was the go-to guy for producers in search of quality supporting players. With so many supporting roles in so many high-profile features, it seemed like only a matter of time before Cannavale came into his own as a leading man.