Hartley spent a few years in karting before moving up to single seaters for the 2002 to 2003 season and the 2003 to 2004 of the Formula First New Zealand where he finished 8th in his first year and 2nd in his second year. From there, he headed to GVI where he competed in the Toyota Racing Series where he took 7 podiums of which 3 were wins to claim 3rd in the standings. He made the move to Victory Motorsport for the 2005-2006 season, taking 8 podiums of which one was a win to finish 8th. Brendon graduated to Formula Renault 2.0 NEC and Eurocup Formula Renault 2.0 where he competed with Motorsport Arena for 14 races each. He placed 10th in the NEC and 13th in the Eurocup. He also joined Mark Petch Motorsport for a single race in the Toyota Racing Series between 2006 and 2007.
He returned to the Eurocup Formula Renault 2.0 Championship with Epsilon Red Bull Team in 2007 where he won the championship with 8 podiums of which 4 were wins. He also raced with the team in Formula Renault 2.0 Italia where he snatched 5 podiums of which one was a win. He also entered his first Masters of Formula 3 with ASL Mücke Motorsport where he finished fourth and his first Macau Grand Prix with Carlin Motorsport where he finished 12th. He returned with Carlin for the two races in 2008 where he finished 5th in the Masters and 3rd in Macau. Full time, Hartley competed with Carlin in the British Formula 3 Championship where he took 11 podiums, of which 5 were wins and 208 points to finish 3rd in the standings. He also raced with both Carlin and RC Motorsport in the Formula 3 Euro Series.
In 2009, Hartley raced full time with Carlin Motorsport once again in the Formula 3 Euro Series where he took 15 points and a single podium to finish 11th in the standings. He also joined the team in the Macau Grand Prix. Brendon then joined Tech 1 Racing in the Formula Renault 3.5 Series where, out of 13 races, he took a single pole, a single podium and 3 fastest laps. He placed 15th in the standings with 26 points. He returned with the team to the series once again in 2010 but only competed with them for 11 races before moving to P1 Motorsport for two races. Collectively, he gained 50 points and 10th in the standings. Hartley also debuted in the GP2 Series with Scuderia Coloni for 4 races, taking a single point and 27th in the standings. For 2011, he headed back to both series once again. He joined Gravity-Charouz Racing for 16 races in Formula Renault 3.5 with 3 podiums and 2 fastest laps; placing him 7th with 95 points and with Ocean Racing Technology in the GP2 Series for four races where he took 4 points and 19th in the standings.
Hartley spent another 4 races with Ocean Racing Technology in 2012. Alongside that, he joined Murphy Prototypes in the European Le Mans Series where he took a fastest lap and a podium to place tenth overall and the LMP2 24 Hours of Le Mans Series which he did not finish. He joined Murphy Prototypes in 2013 for 5 races in the European and 1 in the LMP2. He finished 5th and 6th with 2 podiums and a win in the European Le Mans Series. Hartley also joined Starworks Motorsport for 11 races in the Rolex Sports Car Series where he took two podiums of which one was a win, taking 252 points and 12th in the standings. In 2014, Brendon returned with Starworks for the United SportsCar Championship for a single race to take 55th. He also joined Porsche Team in the FIA World Endurance Championship where he took 3 podiums and 9th in the standings. Hartley also competed in the 24 Hours of Le Mans with the team.
2015 was a much more positive year for Hartley as he competed with Porsche Team for another year in the FIA World Endurance Championship for 8 races where he took 6 podiums of which 4 were wins to take home the championship with 166 points. He also raced with the team for the 24 Hours of Le Mans where he finished second. His luck didn’t continue into the United SportsCar Championship as he finished 30th with Starworks Motorsport. Hartley’s luck also didn’t follow him into 2016 as he stuck with Porche in both championships but finished 4th and 13th. He also debuted in the WeatherTech SportsCar Championship with Ford Chip Ganassi Racing where he finished 27th. 2017 was his final year in the 24 Hours of Le Mans where he joined Porsche LMP Team to win the championship. He also competed in the FIA World Endurance Championship with the team where he took 8 out of 9 podiums, with four being wins to win the championship. Hartley joined Tequila Patron ESM in the WeatherTech SportsCar Championship for a second year where he took a single win and 19th in the standings.
Between 2018 and 2019, he joined SMP Racingfor a single race at the FIA World Endurance Championship where he took a single podium and 18th in the standings. In 2019, Hartley joined Mustang Sampling Racing for the WeatherTech SportsCar Championship for a single race where he took a podiums and 28th in the standings. Hartley is currently competeing in the FIA World Endurance Championship with Toyota Gazoo Racing where he currently sits second in the standing with 5 podiums, of which one is a win.
Brendon made his Formula One debut in 2008 when he joined Scuderia Toro Rosso as a Test Driver. He joined Red Bull Racing and continued with Toro Rosso into 2009 and 2010 as not only a test driver but a reserve driver also. Hartley took a year out in 2011 before joining Mercedes AMG Petronas F1 Team as a test driver in 2012 and 2013. He returned back to Formula One in 2017 for four races with Scuderia Toro Rosso that saw him finish 23rd in the standings. Hartley completed his first full Formula One season the following year when the team changed to Red Bull Toro Rosso Honda where he took four points and 19th in the standings.
FIA Formula E
Hartley debuted in the FIA Formula E Championship this year when he joined GEOX Dragon for the 2019-20 season. He drives in car number 6 alongside team mate, Nico Mueller. As of March 3rd, he sits at 20th in the standings with 2 points after 5 races.