Manthey, a trained mechanical engineer from Bonn, came to motorsport in 1974. Manthey did not complete his apprenticeship in circuit racing in a kart, but in various Simca touring cars. He then switched to Formula Super Vau and finished tenth in the European Cup. From 1981, he returned to touring cars and won the Ford Sport Cup in 1982 and 1983 in his Escort RS 2000.
In the following two years, Manthey drove a Rover Vitesse in the DTM, which was still called the German Production Car Championship at the time. He finished both seasons with the big saloon in second place overall. In 1988, he set a high-speed world record in an Audi 200 Turbo and recorded a first-place finish in the German Porsche Carrera Cup in 1990.
In 1992 and 1993, Manthey again participated in the German Touring Car Championship, in both cases driving an AMG-Mercedes 190 E 2.5-16 Evolution II DTM and, especially in 1993, when he drove for Team Persson Motorsport, almost always achieved finishes in the top ten.
Manthey wrote a special success story with his 22 victories in rounds of the then Endurance Cup at the Nürburgring, all of which he achieved between 1992 and 1995 in his 190 E 2.5-16 Evolution II DTM.
In 1996, the Bonn native founded his Manthey-Racing GmbH and initially became active as team boss in the Porsche Supercup. In the 2001 season, he competed in the German Touring Car Masters with three AMG-Mercedes CLK-DTM cars for Marcel Tiemann, Bernd Mayländer and Patrick Huisman and took third place in the team classification.
Manthey-Racing's main field of activity, however, was the Porsche Supercup and endurance racing with the GT3 Porsche, where the team claimed an almost unimaginable number of victories in the years that followed. At the end of 2015, Manthey retired into private life after 42 years of active motorsport.