Parkes was inspired to race at the age of four when he watched his countryman Wayne Gardner win a race. Gardner would later become his manager. Parkes began racing on dirt tracks a year after his initial inspiration, competed in junior motorcycle speedway, and finished second in the 1997 Australian Under-16 Championship in Adelaide. After switching to circuit racing at sixteen — the minimum legal age in Australia — he won both the Australian 125cc title and the Australian 250cc Production title in 1999, on Honda machinery.
Following his domestic titles, Parkes spent a season in Japan with the Moriwaki squad, finishing third in the All Japan X Formula series. He then moved to Europe to join the NCR Ducati team for the 2001 World Superbike Championship. After a mechanical failure while running strongly in one race, he finished 16th overall. In 2002 he improved to 11th.
Parkes moved to the Supersport World Championship in 2003 with the BKM Honda team, but the team failed to complete the season due to financial difficulties. He joined the prestigious Ten Kate team for 2004 and finished as championship runner-up behind his own teammate Karl Muggeridge.
For 2005, Parkes joined Yamaha's factory team. After a difficult start to the year he ended with a victory to claim fifth overall. The 2006 season saw him challenging for the title before a crash at Assen left him critically injured; he nonetheless returned before season's end to finish third in the standings.
In 2007, Parkes finished a distant second to Kenan Sofuoglu in the championship. He achieved back-to-back victories at Brands Hatch and Lausitzring despite having suffered a broken collarbone early in the season. In 2008, despite recording a series-high six pole positions and winning the season-opening race at Losail, he finished fourth overall.
For 2009, Parkes returned to the Superbike World Championship, joining the factory Kawasaki effort run by Paul Bird Motorsport alongside former Grand Prix winner Makoto Tamada. The team struggled for results, but Parkes delivered an impressive one-off appearance at the British Superbike Championship round at Brands Hatch, qualifying second and finishing second in all three races held there — beaten only by the dominant Leon Camier.
In 2010 Parkes joined the new Echo CRS Honda team, but crashed heavily in pre-season and missed the first three rounds. After returning he was largely a backmarker, and three rounds from the end of the season separated from Echo CRS Honda to join the Motocard Kawasaki team as the replacement for the injured Joan Lascorz. He also competed in World Supersport races at the tail end of that year.
Parkes continued in Supersport racing for 2011 and 2012, riding Kawasaki and Honda machinery and finishing in the top five both years. In 2013 he returned to Australia and won the Australian FX-Superbike Championship with the factory Yamaha team.
In December 2013 it was announced that Parkes would ride for Paul Bird Motorsport in the 2014 MotoGP season alongside Michael Laverty, effectively replacing countryman Damian Cudlin. His participation extended a 31-year streak of Australian representation in the premier class.
For 2015, Parkes rode for Shaun Muir Racing's Milwaukee Yamaha team in the British Superbike Championship until he was forced to withdraw following arm-pump surgery. He then competed in FIM Endurance World Championship races aboard a Yamaha Austria Racing Team machine, capping the year with a one-off MotoGP appearance for ART at the Valencia round, where he retired after completing approximately two-thirds of the race.
Following his competitive career, Parkes continued to race in the FIM Endurance World Championship on a Yamaha YZF-R1.
Broc Parkes is remembered as one of the most durable and well-rounded Australian racers of his era. His runner-up finish in the 2004 World Supersport Championship and his near-title campaigns in 2006 and 2007 established him as a genuine front-runner in the class, while his ability to transition between Supersport, Superbike, MotoGP, and endurance competition demonstrated the versatility that defined his long career.