During 1982, Cappellini was given the chance to try out a Dallara-Toyota Formula 3 car and took pole position in his first race, showing real promise.

Making his debut in the Formula Grand Prix series in 1986, Cappellini started off driving a Mercury-engined Molinari hull, and during the year enjoyed a best result of two fourth-place finishes in Hanover and Singapore.

Guido was narrowly beaten to the title in 1992 with a much-improved boat, as fellow Italian Fabrizio Bocca pipped him to the championship.

From this point Cappellini's form began to decline somewhat within the sport, as other drivers came to the fore, such as Sami Seliö and Jay Price.

Beginning in 2010, Guido has enjoyed moderate success within the class, though for 2013 has stepped aside from driving duties, with Tomaso Polli taking over, due to a dispute over technical regulations, with Cappellini stating that when the rules are even for all the teams, he will gladly re-enter the cockpit.