Gardel came through karting between 1990 and 1995 before stepping up to junior single-seater racing. He entered Formula Ford in 1995 with a best finish of fourth, then competed in the Italian Formula Three Championship from 1996 to 1998, where he was recognised as the best driver under 21 in his debut season. In 1999 he moved to the German Formula Three Championship with the Junior Team Benetton outfit, again recording a fourth-place best result. From 2000 to 2002 he contested the Euroseries 3000 championship, managing only three points finishes across those three seasons, with ninth place as his best championship standing in 2001.
Gardel made his sports car debut in the 2003 FIA GT Championship, sharing a Porsche 911 GT3-RS in the N-GT class with Bert Longin for Freisinger Motorsport. The partnership collected a podium at Donington Park and finished twelfth in the standings.
Promoted to the GT1 class for 2004, Gardel joined BMS Scuderia Italia alongside Matteo Bobbi in a Ferrari 550-GTS Maranello. The pairing took two victories and seven podiums across the season, finishing second in the overall standings — a result that announced Gardel as a genuine title contender.
The title arrived in 2005. Driving for Larbre Compétition with Pedro Lamy as co-driver, the pair built a consistent points haul throughout the season. Lamy was absent for races at Silverstone and Spa, where he was committed to Aston Martin, but the Aston Martins were excluded from points that year, clearing the way for Gardel to claim the championship outright as sole title holder.
Gardel joined the Le Mans Series in 2006, pairing again with Lamy and adding Vincent Vosse to the lineup in an Aston Martin DBR9. The trio won the GT1 class championship with two wins and three podiums total. A fifth-place finish in the 2007 standings followed.
In 2008 Gardel moved to North American competition, racing Daytona Prototypes in the Rolex Sports Car Series with Doran Racing. He also contested the Porsche Carrera Cup Italy in 2009.
Gardel returned to Larbre Compétition for 2010, campaigning the Saleen S7-R in both the Le Mans Series and the Intercontinental Le Mans Cup. He won the GT1 class title in both championships. His 2010 Le Mans campaign brought a GT1 class victory alongside Julien Canal and Roland Bervillé — the first of his two wins at the Circuit de la Sarthe. In 2011 he repeated the feat, this time at the wheel of a Chevrolet Corvette C6.R, winning the GT class and also taking the ILMC class title for a second consecutive year.
From 2012 to 2015 Gardel raced in the Blancpain Endurance Series with Emil Frey Racing, competing alongside appearances in the 2012 International GT Open, the 2013 Italian GT Championship, and the 2014 NASCAR Whelen Euro Series.
Gardel's career arc — from journeyman formula driver to FIA GT champion and two-time Le Mans class winner — reflects the longevity and adaptability that distinguish endurance racing specialists. His 2005 title with Larbre Compétition came under unusual circumstances but was no less earned for it, built on consistency across a full season rather than a single decisive result. His back-to-back ILMC class titles in 2010 and 2011 cemented his status as one of the more accomplished GT1 specialists of his generation.