Kovalainen was born in Suomussalmi, Finland, and began karting in 1991. By 2000 he had won the Nordic karting championship and the Paris-Bercy Elf Masters event, finishing third in the World Formula Super A Championship. He transitioned to car racing in 2001 in the British Formula Renault Championship, claiming Rookie of the Year honors with two wins and two pole positions.
Supported by the Renault Driver Development programme from 2002, Kovalainen moved through British Formula 3, where he again took Rookie of the Year despite finishing third in the championship. He progressed to the Renault-owned World Series by Nissan in 2003 and won that championship in 2004 ahead of Tiago Monteiro, earning the Finnish Driver of the Year award. In the 2005 GP2 Series, driving for Arden International, Kovalainen ran Nico Rosberg close all season, winning races at the Nürburgring, Magny-Cours, and Monza before finishing runner-up in the standings by 15 points.
Renault promoted Kovalainen to a race seat for 2007 to replace Fernando Alonso, who had departed for McLaren. His season opened scrappily but improved through the year; he consistently outperformed teammate Giancarlo Fisichella. The standout moment came at the Japanese Grand Prix at Fuji Speedway, where in treacherous wet conditions Kovalainen held off Kimi Räikkönen across the closing laps to claim second place and his first Formula One podium.
Kovalainen replaced Alonso once more, this time at McLaren alongside Lewis Hamilton. The 2008 season produced his career highlight: at the Hungarian Grand Prix at the Hungaroring, Kovalainen inherited the lead when Felipe Massa's Ferrari retired with an engine failure three laps from the end, and he took the victory — becoming the 100th different winner in Formula One history. He also claimed his first pole position at Silverstone that year. A tyre-wear mismatch with Hamilton's more aggressive driving style was a recurring theme throughout the season, though Kovalainen found partial solutions in the second half of the campaign. He ended 2008 seventh in the championship with 53 points.
The 2009 season was more difficult as McLaren struggled for pace early on. Kovalainen's best result was fourth at the European Grand Prix in Valencia. He ended the year twelfth with 22 points. When Jenson Button signed as Hamilton's teammate for 2010, Kovalainen lost his McLaren seat.
Kovalainen joined the newly formed Team Lotus in 2010 alongside Jarno Trulli. The cars were markedly uncompetitive against the established midfield, and Kovalainen scored no championship points across three seasons with the team, which was rebranded Caterham F1 for 2012. Despite this, he was widely respected for consistently outpacing teammates and rival drivers in similarly backmarker machinery. During the 2011 season he outqualified teammates Trulli and Karun Chandhok in 17 of 19 rounds.
A memorable incident from the 2010 European Grand Prix at Valencia saw Mark Webber's Red Bull launch over the top of Kovalainen's Lotus in a frightening collision; both drivers escaped unhurt.
After Caterham dropped Kovalainen for 2013, he returned to the grid late in the season as a last-minute stand-in for Kimi Räikkönen at Lotus F1, who was recovering from back surgery. Kovalainen raced at the United States Grand Prix and Brazilian Grand Prix, finishing 14th in both.
In 2015 Kovalainen moved to Japan to contest the Super GT GT500 class with Team SARD in a Lexus RC F GT500. In 2016, he and co-driver Kohei Hirate won the championship by taking victory in the season's final round at Twin Ring Motegi after entering the closing double-header fourth in the standings. It was Kovalainen's first championship since the 2004 World Series by Nissan. He continued competing in Super GT until the end of the 2021 season.
Kovalainen also developed a parallel career in Japanese rally competition. He won the Japan Rally Championship JN2 class in 2021, taking class victory in all six rounds. He subsequently moved to the JN1 class in a Skoda Fabia R5.
At the 2004 Race of Champions at the Stade de France, Kovalainen — before he had any Formula One experience — defeated Michael Schumacher and then World Rally Champion Sébastien Loeb in the final to become the first non-rally driver to win the Henri Toivonen Memorial Trophy and the title of Champion of Champions.
In November 2023, following a routine health check, Kovalainen was diagnosed with an ascending aortic aneurysm. He underwent successful surgery and recovered to return to racing.
Kovalainen occupies a specific place in Formula One history as the 100th different race winner, a milestone he secured in Hungary in 2008. His career arc — from Renault's developmental pipeline through a top team to a small constructor — traces the fortunes of a talented driver whose single-lap pace was rated highly; an AWS and Amazon machine learning analysis published in 2020 ranked him the eighth-fastest Formula One qualifier from 1983 to 2020. His subsequent success in Japanese Super GT and rallying demonstrated sustained competitive ability across multiple disciplines long after his Grand Prix career concluded.