He shared the number 22 Martini Racing Porsche 917K with Helmut Marko, winning the 24 Hours of Le Mans in 1971.

The following year Van Lennep won the 1972 Rothmans European Formula 5000 Championship driving a Surtees TS11 and a McLaren M18.

[1] He also drove twice for the Williams GP team, earning his first World Championship point with sixth place in the 1973 Dutch Grand Prix.

With Ensign, he scored a second point in the 1975 German Grand Prix, making him the fifth most successful Dutch Formula One driver behind Max Verstappen, Jos Verstappen, Carel Godin de Beaufort and Christijan Albers.

In 1973, he won the last Targa Florio, sharing the Martini Porsche Carrera RSR with Herbert Müller.