He returned to the FIA GT Championship for the second half of the subsequent year where, driving for Vitaphone Racing alongside Matteo Bobbi, Pier Guidi won the season finale at Zolder and took home fifth in the standings, despite having missed the first three rounds.

Despite 2012 being another patchy year in terms of series participation, Pier Guidi would experience a triumph at the 24 Hours of Spa, where he, Andrea Bertolini, Louis Machiels, and Niek Hommerson came out victorious in the Pro-Am class, driving a Ferrari 458 Italia GT3.

[10] Competing in the GTE class alongside the father-son duo of Alexander Talkanitsa Senior and Junior, Pier Guidi took a win at Imola after battling his way past Marco Mapelli and Andrea Rizzoli and put the team fifth in the championship.

[14] In June, AF Corse included Pier Guidi in their LMGTE Pro effort in the 24 Hours of Le Mans, though the team would be forced to retire due to an engine failure.

[17][18] The year unraveled in triumphant fashion, as seven podiums from nine races, including wins at the Nürburgring, Austin, and Fuji gave Pier Guidi and Calado their first world championship.

[26] With Aston Martin exiting the WEC after 2020, leaving only two manufacturers in the GTE Pro class, 2021 proved to be a season-long battle between the #51 AF Corse Ferrari of Pier Guidi and Calado and the #92 Porsche of Kévin Estre and Neel Jani.

[29][30] Despite voices in the Porsche camp suggesting that Ferrari would have the advantage going into the 6 Hours of Monza, Estre and Jani proved to be victorious, as a chasing Pier Guidi had to pit for fuel with a few laps to go.

Pier Guidi, who pitted for fuel a lap later, came out ahead of Christensen and did not make another attempt to give back the position, and he was also not obliged to do so by the stewards, crossing the line in first and winning the championship.

[36] After Porsche protested the stewards' decision to let the win stand, an official appeal was swiftly withdrawn, thus confirming Pier Guidi and Calado as two-time champions.

[37] During the year, the Italian also scored a personal achievement at the 24 Hours of Spa, winning the race for Iron Lynx with a late overtake on the leading Audi of Dries Vanthoor.

[40] Pier Guidi impressed throughout the year, scoring the marque's sole pole at Monza, putting in important stints at Spa in challenging weather conditions and winning the races in Belgium and Fuji, though his finest drive came at the final round in Bahrain.

[45] The opening round at Sebring proved to be a disappointment, as Pier Guidi collided with a GTE Am Ferrari and finished seventh, meanwhile a brake issue forced the Italian to nurse the car home in sixth at Portimão.