Born on 1 September 1994 in Madrid, the son of two-time World Rally Champion Carlos Sainz, Sainz Jr. began karting in 2006 and won the Formula Renault NEC in 2011 with Koiranen before finishing runner-up in the Eurocup that same year. He then contested British Formula 3, the Formula 3 Euro Series, and FIA European Formula 3 with Carlin in 2012, winning four races in the British series, before moving to the GP3 Series with Arden in 2013. He entered the Formula Renault 3.5 Series alongside his GP3 commitments in 2013 and transitioned to it full-time in 2014.
Sainz raced in Formula Renault 3.5 for the first time in 2013, missing several rounds due to his GP3 commitments. He contested Monaco — where he finished sixth — and selected other rounds through the season, including a seventh-place finish in Hungary's opening race and a sixth place in the season finale at Catalunya. His results were modest but gave him familiarity with the series, teams, and circuits ahead of a full campaign the following year.
For 2014, Sainz switched to DAMS for his first full Formula Renault 3.5 season and immediately became a title contender. He won the second race at the season opener at Monza and followed it with another win at Aragon. At Spa he took two victories in a single weekend. At the Nürburgring he won race one, and at Le Castellet in France he added another win while claiming 50 points from the weekend to build a commanding championship lead.
The title battle with Roberto Merhi gave the second half of the season tension, but Sainz managed the championship effectively, maintaining consistent point-scoring even when not winning. He secured the Formula Renault 3.5 championship ahead of Merhi, and as a reward for his title, Sainz drove the Red Bull RB10 at the post-season test following the 2014 Abu Dhabi Grand Prix.
His Red Bull Junior Team membership dated back to 2010, and his Formula Renault 3.5 title was the trigger for his promotion to a Toro Rosso Formula One race seat alongside Max Verstappen for the 2015 season.
Sainz's Formula One career proved to be exactly the sustained competitive presence his junior record suggested. He debuted at Toro Rosso alongside Verstappen in 2015, then moved through Renault and McLaren before signing with Ferrari in 2021. He took his maiden Formula One win at the 2022 British Grand Prix, added further wins at Singapore 2023, Australia 2024, and Mexico City 2024, and claimed four race victories and 29 podiums in the first eleven seasons of his career. The Formula Renault 3.5 championship of 2014 was the platform on which that career was built, demonstrating an ability to win consistently against strong opposition in one of the most competitive junior formulae of the era.