Santa Monica, California, U.S.
Monaghan first came to national attention in 2003 for his role as Winthrop Paroo opposite Kristin Chenoweth and Matthew Broderick in the ABC television adaptation of The Music Man. When recounting the decision to cast the 9-year-old Monaghan, director and executive-producer Jeff Bleckner explained, "There are some people, when you put them up on film, they sort of pop off the screen at you. That's how it was with Cameron. From the second we saw him, he was it. We were looking for anybody who had that wonderful appeal. And Cameron had it."
In 2004, Monaghan began a recurring role as Chad, one of Dewey's special needs classmates on the Fox comedy series Malcolm in the Middle, which earned him the Young Artist Award as Best Young Television Actor in a Recurring Role. The following year, he began a recurring role as Palmer Noid on the Nickelodeon situation comedy Ned's Declassified School Survival Guide. Subsequent guest-starring television roles followed, including appearances on Criminal Minds, Numb3rs, The Mentalist, Monk, Three Rivers, Fringe, The Glades, and Terriers.
In 2005, Monaghan transitioned to theatrical film roles, appearing as Timmy in the independent western Brothers in Arms. The following year, he appeared as Kevin O'Doyle, the bothersome next-door neighbor to Adam Sandler in the fantasy comedy Click. A series of subsequent feature film roles followed, including appearances in The Santa Clause 3: The Escape Clause, Dog Gone, Safe Harbor and Another Harvest Moon, as well as portraying the boy detective Bob Andrews in the Three Investigators film series.
In April 2010, Monaghan was cast as a principal ensemble cast member on the Showtime comedy-drama series Shameless. On the series, which premiered in January 2011, Monaghan portrays Ian Gallagher, the gay teenage son of a large dysfunctional Chicago family. Sarah Hughes of The Independent commended Monaghan's portrayal for providing "one of the more nuanced depictions of a gay teenager to be seen on US TV."Matthew Gilbert of The Boston Globe described Monaghan's performance as "extraordinary." And the gay-interest media outlet AfterElton.com cited Monaghan's portrayal of Ian in naming him to its list of "2011's Break-Out TV Actors". In February 2014, Showtime announced it had renewed the series for a fifth season, scheduled to begin airing in 2015.
Concurrent with his role on Shameless, Monaghan has continued to appear in a variety of episodic television roles. In 2011, he guest-starred as Nick Peyton, a teenage boy accused of murdering his Marine father, on the CBS crime series NCIS. That same year he appeared as Jonathan McKenna on the TNT mystery series Rizzoli & Isles. In 2012, he guest-starred as Eddie Sandow, a 19-year-old who creates a hostage situation after his father is accused of sexual assault, on the NBC crime series Law & Order: Special Victims Unit.
In addition to his television credits, Monaghan has continued to appear in a variety of feature film roles. In 2011, he co-starred as high school sophomore Corey Doyle in the Disney teen drama Prom. In 2012, he portrayed Jake, the son of an attractive YMCA director in the sports themed comedy 2nd Serve. In 2014, Monaghan starred as Adam McCormick, a small-town high school athlete who becomes consumed by the death of one of his classmates in the independent drama Jamie Marks Is Dead. That same year, he appeared as Mason Ashford, the best friend and romantic interest to Rose in the fantasy adventure film Vampire Academy. He also starred as Asher in the dystopian movie The Giver, alongside Brenton Thwaites, Odeya Rush, Jeff Bridges and Meryl Streep. In 2015, he appeared in Gotham as Jerome, with speculation his character was that of the future Batman's nemesis The Joker, although this would be cleared up early in the second season of the series.
2002 The Wishing Stone
2005 Brothers in Arms
2005 Desperate Hippies
2006 The Santa Clause 3: The Escape Clause
2007 The Three Investigators and the Secret of Skeleton Island
2008 Dream Machine
2008 Dog Gone
2009 Safe Harbor
2009 The Three Investigators and the Secret of Terror Castle
2010 Another Harvest Moon
2010 Two Boys
2010 Bad Bunny
2012 2nd Serve
2014 Jamie Marks Is Dead
2014 Vampire Academy
2014 The Giver
2016 Amityville: The Reawakening
2003 The Music Man
2005 The Adventures of Tango McNorton: Licensed Hero
2004–2005 Malcolm in the Middle
2005 Avatar: The Last Airbender
2005–2006 Ned's Declassified School Survival Guide
2006 Criminal Minds
2007 Shorty McShorts' Shorts
2009 James Gunn's PG Porn
2009 The Mentalist
2009 Safe Harbor
2009 Three Rivers
2010 The Glades
2011 Rizzoli & Isles
2012 Law & Order: Special Victims Unit
2016 Mercy Street