Having worked as a child actor in such projects as the TV-movie drama "A Voyage Round My Father" (1982) and the popular school-set soap "Grange Hill" (BBC), Maguire worked steadily as a child actor, but would garner much greater popularity as a teen. Though his role on "EastEnders" lasted for only one full year, Maguire and his endearing Aidan made quite an impression on audiences, and when the well-meaning but ultimately troubled young character returned to his home in Ireland, fans were distraught. Lucky for them Maguire had no plans to leave the public eye, but rather was embarking on a pop music career. With eight hits in the British Top Thirty during in his three-year stint as a singer, Maguire was pretty successful and stayed in the pages of the teen fan magazines, but failed to make it big or cross over to a wide audience in a market flooded with attractive pop artists.
In the midst of his recording career, Maguire had a featured role in the British TV series "Dangerfield", playing the son of the eponymous detective in 1995. The end of the decade saw Maguire, now no longer a cute baby-faced teen, emerge with a leaner and somewhat more dangerous look well-suited to the types of slick rogues he would find himself frequently and convincingly playing. 2000 saw him return to series television with a role as a dashing bachelor in the comedy "Sunburn", a type he would revisit in his US series television debut "Off Centre" (The WB, 2001- ). Here he played Euen, a decadent British womanizer who shows the ropes to Eddie Kaye Thomas' more neurotic American Mike. The show would introduce the actor to a new audience, one he would revisit in 2002, played the decidedly different-tempered "Prince Charming" in a TNT original romantic comedy TV-movie.
Having previously appeared with small supporting roles in features including 1992's "Waterland", Maguire made his feature starring debut in "Out of Depth", a 1999-lensed gritty independent drama released in Great Britain in 2001. Playing a young man from rough beginnings who turns his life around, Maguire proved himself a gifted actor, more than capably handling the emotions surrounding his self-made man's descent into the thug life after getting embroiled in a violent scheme of vengeance and drug pushing. Positive notices surrounded both the film and its star, and Maguire could hope for a bright future on the big screen in addition to his flourishing television career.