Monaghan originally auditioned for the role of Sawyer.The role of Charlie was then changed from an old, washed up rocker from the 1980s, to a young one-hit wonder to accommodate Monaghan's age.He is also fond of working the New York Times crossword puzzle.
Monaghan narrated Ringers: Lord of the Fans, a documentary about The Lord of the Rings fandom.He also provided the narration for The Discovery Channel's documentary Devil's Bible in 2008.Monaghan has a great love for insects and reptiles that he developed during his childhood, and has kept an assortment of pets, including a leaf-mantis named Gizmo, a black widow spider named Witchitar and an albino snake named Blink.An avid outdoorsman, Monaghan enjoys activities such as surfing, kayaking, snowboarding, football, basketball and hiking.He is a longtime fan of hometown English Premier League football team Manchester United since his childhood, despite his father being a fan of Manchester City.
Monaghan loves to play various games, and has hosted game nights for fellow cast members in the past.
He currently hosts the nature program Wild Things with Dominic Monaghan (2012–present).
Monaghan's family lived in Berlin, Düsseldorf, Stuttgart and Münster, moving about every four years.
Monaghan is a fan of The Gaffer Tapes: Fantasy Football Podcast and has appeared as a guest in both April and November 2016, as well as submitting several audio questions which are played on the podcast.
While appearing as a guest, Monaghan stated "It's the best fantasy football podcast out there".
Although Monaghan held many occupations when he was younger, he always wanted to be an actor. Anne's, Monaghan became a regular in school plays such as Oliver Twist, A Christmas Carol and Bugsy Malone before joining the Manchester Youth Theatre.