He made his AFL debut for the Melbourne Football Club in Round 9, 1998, against Essendon.
Longmuir played a total of 17 games for Melbourne in 1998 and 1999 before being traded to Fremantle at the end of the 1999 season in exchange for the club's second-round draft pick (#19 overall).
During this time, he was also a part of West Perth's 2003 WAFL premiership team, where he played when not selected for Fremantle.
Following the 2004 AFL season, Longmuir was traded by Fremantle to Carlton, in exchange for a fifth-round draft pick[1] (#67 overall).
In 2006, he started the season with the Bullants, and he broke back into the Carlton senior team in Round 10 against Port Adelaide; however, he was injured in the first quarter and did not play again until the VFL finals.