Karting (1991–2000)

Kovalainen's career began in kart racing, much like that of many other Formula One drivers. He competed in karting from 1991 to 2000, during which time he finished runner-up in the Finnish Formula A championship in 1999 and 2000. In 2000 he won the Nordic championship and the Paris-Bercy Elf Masters event, as well as finished third in the World Formula Super A Championship, leading him to be elected as the Finnish Kart Driver of the Year.

Formula Renault (2001)

Kovalainen began his car racing career in the British Formula Renault Championship, which fellow Finn Kimi Räikkönen had won in 2000 before moving straight into Formula One with Sauber. Kovalainen's apprenticeship in the junior categories of motor sport was more conventional, but he used Renault power at every step along the way. He finished fourth in the championship with two wins, two pole positions, five podiums and three fastest laps, earning the Rookie of the Year award. He also took part in the Formula Three Macau Grand Prix, where he finished eighth.

Formula Three (2002)

Kovalainen attracted the support of the Renault Driver Development programme and in 2002 moved up to the British Formula Three Championship with Fortec Motorsport who used Renault engines. He became one of the most competitive drivers on the grid by the second half of the season and all five of his wins came in the final nine races. With three pole positions and three fastest laps, Kovalainen finished third overall in the championship behind Robbie Kerr and James Courtney and he was again Rookie of the Year.

He also demonstrated strong form in the international non-championship rounds, with second place in Macau and fourth place at the Marlboro Masters at Zandvoort.

World Series by Nissan (2003–2004)

Kovalainen moved into the Renault-owned World Series by Nissan in 2003 – but faced a tough team-mate at the Gabord team in Franck Montagny. Montagny had already spent two seasons in the World Series and had won the championship in 2001. Montagny won the 2003 title with nine wins to Kovalainen's one.

Kovalainen continued in the series in 2004, but moved to Pons Racing, where he won the championship ahead of Tiago Monteiro, with 192points and six wins. With Kimi Räikkönen finishing seventh in Formula One and Marcus Grönholm fifth in the World Rally Championship, Kovalainen was awarded as the Finnish Driver of the Year.

GP2 Series (2005)

In 2005, Kovalainen entered the GP2 Series, the new 'feeder' series for F1 and the successor to Formula 3000. Driving for the Arden International team, Kovalainen began the season with strong results by winning the first round of the championship in Imola and then finishing third in the sprint race. In Barcelona he scored his third consecutive podium, but in the sprint race his car stalled on the grid. He dominated the race in Monaco by claiming pole position, leading the race for the first 21 laps and clocking the fastest lap of the race. Problems during his pitstop, however, dropped him down to fifth. At the Nürburgring he gave his best performance yet, by winning the race from 17th on the grid. In the sprint race José María López caused a collision which forced Kovalainen to retire. At Magny-Cours he won again from fourth on the grid, and came third in the sprint race.

At this point in the season, however, a resurgent Nico Rosberg with his ART Grand Prix team seemed to find more speed and began scoring victories, emerging as Kovalainen's main rival for the championship. Kovalainen and Arden fought back, scoring podiums and points positions in Silverstone, Hockenheim and Hungaroring, but were unable to find the necessary speed to beat Rosberg. In Istanbul's feature race Kovalainen finished tenth due to engine problems, but in the sprint race held in wet conditions he returned to his winning ways. At Monza Arden were fast again, and Kovalainen snatched his second pole of the season and won the feature race. In the sprint race he could only manage fifth position, however, and this meant that with four races left in the season, Kovalainen was leading Rosberg by only four points.

After a chaotic weekend at Spa affected by rain and Safety Cars, Rosberg took the lead from Kovalainen. In the final two rounds in Bahrain, Rosberg and ART seemed to be unmatched again, and he secured the championship by winning the feature race with Kovalainen finishing third. Retiring from the last sprint race, Kovalainen finished runner-up in the series, 15 points adrift.

Renault 2004–2006

Kovalainen, Franck Montagny and José María López tested the Renault R23B F1 car at Barcelona in December 2003. Kovalainen also tested for Minardi, but Renault made him second test driver alongside Montagny for 2004.

Kovalainen was promoted in Montagny's place at the end of 2005 and spent the 2006 season in a full-time testing role, logging over 28,000 km of testing.

Renault's lead driver Fernando Alonso had signed for McLaren for the 2007 season, and Renault elected to promote Kovalainen in his place, which they confirmed on 6 September 2006. Team boss Flavio Briatore said: "With Kovalainen, I hope to find the anti-Alonso."