In 1997 Maguire left Canberra and signed for the new Adelaide Rams club in the breakaway Australian Super League competition.

He made his début at fullback in the Rams inaugural game against the North Queensland Cowboys in Townsville which Adelaide lost 24–16.

[citation needed] When Maguire retired from playing he initially left the game and taught physical education before signing as a strength and conditioning coach for Canberra.

Maguire was an integral part in Melbourne's stripped NRL premierships and took control of first team affairs when head coach Bellamy took up representative duties for the Blues in State of Origin.

[5] He was heavily linked with a move to English club Wigan Warriors towards the end of the 2009 season and signed a three-year deal with the Super League side on 7 October 2009.

Maguire then recorded his biggest victory as a Wigan coach, beating nearest rivals St. Helens in the last ever Good Friday derby match at Knowsley Road.

[8][9][10][11][12][13][14][15][16][17][18][19][20][21] The following February his Wigan side took on 2010 NRL premiers St. George Illawarra Dragons in the 2011 World Club Challenge but were defeated.

In 2011 Maguire announced his resignation from Wigan, in order to replace the retiring John Lang as head coach of National Rugby League club the South Sydney Rabbitohs for the 2012 NRL season.

[39] The Rabbitohs performed well during the 2012 NRL season with Maguire credited for the successful move of Greg Inglis from centre to full-back.

Unlike the last round of the ordinary season, Souths overcome an early 12–0 deficit to score 32 unanswered points, eventually winning the match 32–22.

In his first year in charge of the Wests Tigers, Maguire guided the club to a ninth-place finish narrowly missing out on the finals.

In the post match press conference, Maguire spoke to the media saying I'm sick and tired of the ups and downs of the performances.

[43] During the half-time interval in round 12 of the 2020 NRL season, Maguire was seen on a dressing room camera berating his players for their poor first half performance against the New Zealand Warriors.

[45] In the 2021 NRL season, Maguire guided the Wests Tigers to a disappointing 13th placed finish on the table including a 38-0 loss against Wooden Spoon side Canterbury in the last round.

New Zealand had won just one game against the Kangaroos in the previous nine outings, with a run of three-straight losses including an 18-point drubbing just a week earlier.