King began his motorsport career in 2005 in karting, where he was active until 2010. Among other things, he was in 2009 Asia- Pacific KF3 Champion. In 2010, he also gave his Formula racing debut at the season finale of the Formula Palmer Audi. King immediately secured a pole position and finished the race in second place. In the overall standings, he was 23 He subsequently moved to Manor Competition and participated in the British Formula Renault Winter Cup. This he finished in 15th place overall. In 2011 he started for Manor Competition in the British Formula Renault. With a second place finish in the season, he scored the best finish of his racing team. He finished the season in eighth championship course. He then joined for Manor Competition also in the winter series. In this he was twelfth. In addition, King 2011 took part in the FIA Formula 2 Championship at six races. He became the youngest driver to go this category. By the end of 2009, he completed his first Formula 2 test drive. King scored in four of these points race and a fifth place was his best result. At the end of the season he was on the 14th place overall. He also rose to the second half of the season in the North European Formula Renault, where he started for MP Motorsport. With a second place as best result and a total of four podium finishes, he finished tenth in the drivers' standings.
Early 2012, King went for M2 Competition in the Toyota Racing Series, the highest single-seater racing series in New Zealand, at the start. He won a race and stood on the podium four times. At the end of the season he was on the fifth place in the overall standings. Then King went for Manor MP Motorsport, a collaboration between Manor Competition and MP Motorsport in the Formula Renault 2.0 Eurocup at the start. With a third place as the best finish he finished the season in 13th place overall. King has also participated for Manor MP Motorsport at the North European Formula Renault. He won a race and was nine times on the podium. With 316 to 376 points, he defeated Jake Dennis and was runner-up. 2013, King moved to Carlin in the European Formula 3 Championship. With four podium finishes King was sixth in the drivers' standings. He defeated his teammate Harry Tincknell, who finished fifth overall with a race win. In addition, King 2013 Carlin took part in the British Formula 3 Championship. With four wins and eight podium finishes in twelve races he chose the title for themselves. With 176 to 135 points he won against Antonio Giovinazzi.
Kings father Justin King is CEO of the UK supermarket chain Sainsbury's.
- 2005-2010: Karting
- 2010: Formula Palmer Audi ( # 23 )
- 2010: British Formula Renault Winter Series (No. 15)
- 2011: British Formula Renault (8th place )
- 2011: North European Formula Renault ( 10th place )
- 2011: Formula 2 ( 14th)
- 2011: British Formula Renault Winter Series (No. 12)
- 2012: Toyota Racing Series ( 5th place)
- 2012: Formula Renault 2.0 Eurocup ( 13th)
- 2012: North European Formula Renault (2nd place)
- 2013: European Formula 3 ( 6th place)
- 2013: British Formula 3 (Master)