Maguire’s first credited published comics work was The Official Handbook of the Marvel Universe vol. 2 #6 in 1986. He debuted at DC Comics with artwork in Who’s Who: The Definitive Directory of the DC Universe #23 and 25. In 1987, Maguire was the artist on the relaunch of Justice League written by Keith Giffen and J. M. DeMatteis. Maguire left the series with issue #24 (February 1989) but returned for Giffen and DeMatteis’ final story in #60 (March 1992). The two writers and Maguire reunited in 2003 for the Formerly Known as the Justice League miniseries and its 2005 sequel, “I Can’t Believe It’s Not the Justice League” published in JLA Classified. Maguire’s collaborations with Giffen and DeMatteis include The Defenders at Marvel in 2005, a DC Retroactive: Justice League – The ’90s one-shot in 2011, and the Metal Men back-up stories in the 2009 revival of the Doom Patrol.
Maguire was one of the artists who launched the Team Titans series in 1992. He has frequently collaborated with writer Fabian Nicieza on series such as Adventures of Captain America, X-Men Forever, and Batman Confidential.
Maguire and George Pérez alternated as artists of the revival of the Worlds’ Finest series, which was written by Paul Levitz. Maguire was to have reunited with Giffen and DeMatteis on the Justice League 3000 series but was removed from the project by DC. Maguire and writer Marc Andreyko became the creative team on Supergirl vol. 7 as of issue #21 in August 2018.