D'Agosto's big break came when he was cast as the ethical committee chairman Larry Fouch in the dark teenage comedy
Election (1999), while he was still a senior at Creighton Prep. The film was written and directed by
Alexander Payne, another alumnus of Creighton Prep. D'Agosto starred in the film
Psycho Beach Party (2000) while still in college. In 2002, he moved to Los Angeles to pursue a full-time acting career. He landed guest appearances on primetime television series such as
Boston Public,
ER,
Six Feet Under,
Cold Case,
House,
Supernatural, and
Without a Trace. He appeared in three episodes of
The Office. He also played West Rosen on the series
Heroes. To prepare for the film
Fired Up!, D'Agosto spent three weeks at a cheer camp and worked with a professional choreographer. He also starred in
From Prada to Nada with
Camilla Belle, which is loosely based on
Jane Austen's
Sense and Sensibility. In 2011, he starred as Sam Lawton in
Final Destination 5. In Fall 2012, D'Agosto played the role of Tony Kirby in ''
You Can't Take It with You''. As of 2013, D'Agosto co-starred in
Showtime's Masters of Sex as
obstetrician Dr. Ethan Haas, fictional protégé of pioneering sex researcher Dr.
William H. Masters (of
Masters and Johnson fame). His character is a composite of two of Masters' actual associates. To prepare for the part of Dr. Haas, in addition to reading the biography that
Masters of Sex is based on, D'Agosto read
The Fifties by
David Halberstam. He also watched movies from the 1950s and documentaries on journalist
Edward R. Murrow, which had a lot of "individual footage of interviews with these sort of everyday people from that time period." In late 2014, he appeared on ''
Grey's Anatomy'' playing the OB/GYN surgical resident Graham Maddox. He left the show late November 2014 in the episode 'Risk'. D'Agosto was cast in early October 2015 in the role of
Harvey Dent in the television series
Gotham. In 2017, D'Agosto starred in the lead role in NBC's mockumentary legal comedy series,
Trial & Error. Season 2 wrapped in August 2018. In November 2022, D'Agosto has a recurring role as Deputy Director Doug Bailey in
Criminal Minds: Evolution. ==Personal life==