A car trader from Frauenfeld in Switzerland, Vonlanthen began racing in Formula Vee in 1968 and, driving a Tecno, won the 1972 Swiss F3 championship.
He went into Formula 2 in 1973 with a GRD, taking a third place in the Rome GP, but this was easily his best result until he came second in the opening round of the 1975 series at Estoril in a March 742-BMW, when most of the front-runners fell by the wayside.
His brief Formula 1 career lasted just three races in 1975, Jo driving a works Ensign in the International Trophy before switching to Williams for the Swiss GP at Dijon. After taking a distant 14th place in this non-championship race, Vonlanthen made the grid in his Williams for the Austrian GP only because both Henton and Wilson Fittiplaldi had practice mishaps.
He returned to Formula 2 on an irregular basis in 1976, but never really featured.