Maguire’s first credited published comics work included pages for The Official Handbook of the Marvel Universe vol. 2 and Who’s Who: The Definitive Directory of the DC Universe. 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 Defenders 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 with collaborated writer Fabian Nicieza on series such as Adventures of Captain America, X-Men, and Batman Confidential.
Maguire and George Pérez alternated as artists of the revival of the Worlds’ Finest series, which is 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.