Born in Finland in 1969, Lehtinen took up co-driving in 1988, initially alongside friend Jari Mikkola. He developed his skills in domestic competition before stepping up to the international stage, building a reputation as a precise and reliable navigator in an era when Finnish talent dominated the sport.
Lehtinen partnered Marko Ramanen in the Finnish Rally Championship, and made his World Rally Championship debut at the 1997 Rally Finland. In 1999, the Lehtinen–Ramanen pairing competed in the British Rally Championship, while Lehtinen also accompanied Jouni Ampuja to sixth place in Group N at the Finnish Championship. He continued working with Ampuja in the Finnish Championship for a further two seasons.
In 2002, Lehtinen took on a gravel crew role for Škoda driver Toni Gardemeister on the world championship circuit, broadening his technical experience. During the same period he began working with Mikko Hirvonen on international events, a partnership that would define the central chapter of his career.
Lehtinen and Hirvonen competed together on all their WRC outings from 2003 onward, initially with Subaru in 2004 before joining the Ford World Rally Team in 2006. The pair immediately made their mark at the top level: Lehtinen claimed his first WRC victory at the 2006 Rally Australia. Over the following years the partnership became one of the most consistent and competitive pairings in the championship.
The 2008 season proved their strongest, with Hirvonen and Lehtinen finishing as championship runners-up — the closest either man came to a drivers' title. Their campaign included multiple victories and demonstrated that the Ford Fiesta-era team could mount a sustained title challenge.
The duo moved to Citroën Total in 2012, adding the French manufacturer's entry to their growing list of team affiliations. Their 15 WRC victories together represent a significant record in the co-driving discipline, reflecting both Lehtinen's navigational accuracy and his ability to adapt across different car platforms and team environments.
After the close of the Hirvonen partnership, Lehtinen continued co-driving at international level. As of 2019, he was paired with M-Sport Ford driver Teemu Suninen, demonstrating his continued relevance in the WRC paddock and his ability to form effective partnerships with drivers of the next generation.
Jarmo Lehtinen's career is emblematic of the Finnish school of co-driving — disciplined, technically proficient, and built around long-term driver partnerships rather than frequent team changes. His 15 WRC victories with Hirvonen place him among the most successful co-drivers of the 2000s, and his debut at the 1997 Rally Finland through to his continued activity nearly 25 years later reflects an enduring commitment to the craft. In an era dominated by Finnish drivers, Lehtinen was the quiet but essential partner whose work behind the pace notes made those results possible.