He was the sixth-place finalist on the fourth season of the reality television series American Idol, and received a nomination for the Tony Award for Best Performance by a Leading Actor in a Musical for his role in Rock of Ages.

[7] Some years before appearing on American Idol, Maroulis competed on the dating show Elimidate[8] and was an extra in Law & Order: Special Victims Unit and a voice-over artist on the Astro Boy.

After graduating from the Conservatory, Maroulis trained as an acting apprentice at the prestigious Williamstown Theatre Festival[10] in the Berkshires of Western Massachusetts and performed as Roger Davis in the Broadway international touring company of Rent.

[14] Less than a week before his elimination, Maroulis's pre-Idol band, Pray for the Soul of Betty, announced the 10 May release of their self-titled debut on their label, Baby Julius.

His set list included songs he had performed previously in his theatre roles, from Hedwig and the Angry Inch[22] Rent, and Jesus Christ Superstar,[23] as well as from his stint on American Idol.

In August 2006, Constantine completed a solo tour of 13 cities, where he debuted material to be featured on his upcoming CD, including various self-penned compositions.

[27] He has sung the Anthem at additional sporting events, including at the Reality All-Star Soccer Festival (organized by Survivor: Africa winner, Ethan Zohn) in April 2007,[28] as well as before the start of a 49ers/Bengals football game at Monster Stadium, San Francisco in December 2007.

[31] On July 4, 2009, Maroulis sang the National Anthem at the official ceremonies to re-open the Statue of Liberty's crown to the public, for the first time since its closure after 9/11.

[32] Maroulis (supported by Ben Phillips, guitarist/vocalist for the NYC-based bands Famous and The Pretty Reckless) embarked on another solo tour in February 2008,[33] playing to sold-out venues in Boston, Philadelphia, New York City, Annapolis, Maryland, and Los Angeles.

Maroulis has been a regular contributor to the Loukoumi series of children's books by author Nick Katsoris, providing the voice of Gus the Bear.

Maroulis partnered with Scott Bradlee's band Postmodern Jukebox in early 2018 and performed a number of concerts with them around the United States and Canada.

In the fall of 2005, Maroulis was in negotiations to star in a television sitcom called Brooklyn that was to be loosely based on his upbringing as the youngest of three in a large Greek-American family of New York.

[51] Along with the other cast members, he contributed a recording of the Adam Sandler "Hanukkah Song" to the 8th Carols for a Cure CD to help raise funds for the Broadway Cares/Equity Fights AIDS organization.

Beginning on January 9, 2007, Maroulis took over the role of "Young Soldier" in the Off-Broadway musical revue, Jacques Brel is Alive and Well and Living in Paris[52] where he performed through the end of February.

Later that year, Maroulis joined the cast of The Bold and the Beautiful for a limited run as Constantine Parros, a singer and record producer,[53] a role created specially for him.

[54] His next major role occurred that June, when Constantine starred as Judas Iscariot in the Premier Theatre Company's production of Jesus Christ Superstar.

[67] Maroulis was cast as Melvin Ferd the Third, in The Alley Theatre's production of The Toxic Avenger, which performed in Houston, Texas, from January 13, 2012, through February 12, 2012.

[68] The Houston Chronicle praised the production as being "brilliant," adding that "[the] casting is nothing short of miraculous" and "Mr. Maroulis' voice is a gorgeous, crystal-clear, unwavering, bright tenor instrument that will blow you away.

[70] In autumn 2012, Maroulis took on the title role(s) in Frank Wildhorn's Jekyll and Hyde, co-starring with Deborah Cox,[71] which arrived on Broadway after a 25-week national tour.

Maroulis has guest starred on various television programs including Law & Order: Special Victims Unit, Z Rock, Unforgettable, and Madam Secretary, as well as web series such as Mozart in the Jungle and Kittens in a Cage.

On July 23, 2014, it was announced that Maroulis would be returning to Rock of Ages as Drew for a twelve-week engagement at the Helen Hayes Theater beginning August 4, 2014.

[81] In March 2017, Maroulis joined The Most Beautiful Room in New York as Sergio, which had its world premiere in May 2017 at Long Wharf Theatre in New Haven, Connecticut.

[83] That summer, Maroulis was cast as Che in Evita at North Shore Music Theatre in Beverly, Massachusetts, running from September 26 through October 8, 2017.

[90] In 2024, Maroulis starred in World Premiere of New Musical East Carson Street at Axelrod Performing Art Center's new Bell Theater.

[96] On July 1, 2009, after a matinee performance of Rock of Ages, Maroulis and the rest of the cast set a new Guinness World Record for the Largest Air Guitar Ensemble.

A total of 810 participants, including audience members and fans, shattered the previous record of 440 people playing air guitar simultaneously.

[99][100] A month later, the Rock of Ages star was immortalized in a second portrait; this time joining the ranks of the famous on the Broadway Wall of Fame at Tony's di Napoli, also in New York City.

[108] On December 23, 2010, Maroulis and his then girlfriend, former Rock of Ages chorus girl co-star Angel Reed, welcomed the arrival of their daughter, Malena James Reed-Maroulis.