Sainz Jnr. inherited his passion for motor sport from his father, but instead of the narrow roads and dirt tracks, he chose the race track, starting in karts at the age of eleven. He made his single-seater debut in 2010 in Formula BMW, taking his first win at Silverstone with the Euro International team. The following year, he moved to Formula Renault, racing for Korainen Motorsport, winning ten times on his way to the Northern Europe Cup title. In 2012, he stepped up to European Formula 3 with the Carlin team, taking a win at Spa-Francorchamps and finishing the championship in fifth place. The following year, he raced in Formula Renault 3.5 winning the 2014 title with the DAMS team, taking seven wins and seven poles, to finish ahead of Frenchman Pierre Gasly.

This performance opened the door to Formula 1 and he made his debut with Scuderia Toro Rosso in the 2015 Australian Grand Prix, teamed with Max Verstappen, scoring 2 points on his maiden outing. He picked up a further 16 points that season and was 15th in the championship. The following year, he had his first encounter with Ferrari as his Toro Rosso was fitted with a Maranello-made power unit. Carlos ended the year 12th in the championship on 46 points and in 2017, he continued to progress, making it into the top ten, finishing ninth, after switching from Toro Rosso to Renault for the final four races of the year and for 2018. The Spaniard was tenth with the French team and his best result was a fifth place in Azerbaijan.

In 2019, Sainz joined McLaren, putting in a solid performance, which ended with sixth place in the championship, claiming his first podium in a thrilling Brazilian Grand Prix. He stayed with the English team the following year, again finishing in sixth place and coming close to winning the Italian Grand Prix, finishing second behind Gasly. A really solid driver, Carlos always gets the most out of his car and is noted in the business for his ability to help engineers develop the car.

Sainz is the third Spaniard to race in Formula 1 with Scuderia Ferrari, after Fernando Alonso (96 GPs with the team from 2010 to 2014) and Alfonso de Portago (5 GPs from 1956 to 1957). The Maranello marque has also employed two Spaniards as test drivers: Pedro de la Rosa e Marc Gené.