In 1989, Lomax, alongside his three brothers, played for Wainuiomata in their Wellington Rugby LeagueGrand Final win over Upper Hutt. In 1990, Wainuiomata won the Wellington Rugby League and the national Lion Red Cup competitions. That year, he represented the New Zealand Māori team against Great Britain. He later played at the 1992 Pacific Cup. In 1992, Lomax and his three brothers represented Wellington against Bay of Plenty. All four brothers later played in the Lions 25–18 national Grand Final win over the Northcote Tigers. In 1993, he was invited to be part of an Auckland Invitational XIII side that drew 16-all with the Balmain Tigers.
Canberra Raiders
In 1993, Lomax moved to Australia, joining the Canberra Raiders in the NSWRL Premiership. In Round 1 of the 1993 NSWRL season, he made his first grade debut in Canberra's 8–22 loss to the St George Dragons. In his debut season for the club, he played 20 games, starting all 20 at. In June 1993, he made his debut for New Zealand, playing in their three-game series against Australia. At the end of the year, he was selected to go on the 1993 New Zealand rugby league tour of Great Britain and France, playing in all five test matches. In 1994, Lomax played 23 games for the Raiders and won the club's Player of the Year award but missed their Grand Final win over the Canterbury-Bankstown Bulldogs due to suspension. A week earlier, he was sent off and charged for a high shot on Billy Moore in the side's 22–9 preliminary final win over the North Sydney Bears. In 1995, he played just 10 games for the Raiders but captained New Zealand for the first time in their mid-season series against France. On 23 June 1995, he captained New Zealand for the third and final time in a 8–26 loss to Australia. In October 1995, he represented New Zealand at the 1995 Rugby League World Cup, playing one game. In Round 12 of the 1996 ARL season, Lomax collected Parramatta's Adam Ritson with a high tackle, knocking him out. Following the incident, a routine scan discovered that Ritson had a life-threatening brain cyst, from which he would never fully recover, ending his career.
North Queensland Cowboys
In 1997, Lomax signed with the North Queensland Cowboys, joining his former Raiders' head coachTim Sheensat the club. In his first season at the Cowboys, he played 15 games, missing three weeks due to suspension. That year, he became the club's first New Zealand international when he played in the Kiwis' 30–12 win over Australia. In 1998, he took over as captain of the Cowboys and won the club's Player of the Year award. On 24 April 1998, he started at prop for the Kiwis in their 22–16 ANZAC Test win over Australia, his last game for his country. In 1999, Lomax played just eight NRL games due to injury.
Melbourne Storm
In 2000, Lomax moved to the Melbourne Storm, playing just three games for the club before retiring at the end of the season.
