Gardemeister first attracted attention by winning the Finnish Rally Championship Group A title (under 2000 cc) in 1997 driving a Nissan Sunny. He earned limited WRC outings with SEAT in 1998 aboard the Ibiza, and by 2000 had secured a full-time seat in the Córdoba WRC alongside former world champion Didier Auriol. Early highlights included third place in New Zealand in 1999 and fourth at the 2000 Monte Carlo Rally.
When SEAT withdrew from works competition for 2001, Gardemeister moved to privateer machinery, scoring points at both the Monte Carlo and Swedish rallies in a Peugeot 206 WRC. He also received call-up drives with Mitsubishi Ralliart in Finland and New Zealand that season.
Those performances brought Gardemeister to Škoda, where he drove the Octavia WRC through 2002 and 2003, again partnering Auriol, before moving to the Fabia WRC in 2004. His best results with the Octavia were fifth-place finishes at Rally Argentina 2002 and Rally New Zealand 2003. With the Fabia he recorded seventh at the 2004 Rallye Deutschland.
Gardemeister joined the BP Ford World Rally Team for 2005 and delivered his most competitive WRC campaign. He finished second on his debut at the Monte Carlo Rally, third in Sweden — briefly leading the drivers' championship — and added a second place at the Acropolis Rally and a further second in Corsica behind Sébastien Loeb. He closed the year fourth in the drivers' standings, scoring twice as many points as team-mate Roman Kresta. Despite this performance, Ford signed Marcus Grönholm and Mikko Hirvonen for 2006, leaving Gardemeister without a factory seat.
For 2006, Gardemeister drove for the privateer Astra Racing team in a Peugeot 307 WRC with co-driver Jakke Honkanen, finishing third at the Monte Carlo Rally on the season opener. He went on to use a Citroën Xsara WRC for three further rounds, picking up fourth in Greece and Germany and fifth in Cyprus. In 2007, he contested five rallies in a Mitsubishi Lancer WRC05, recording seventh in Monte Carlo and sixth in Sweden and Sardinia, then drove a Xsara to seventh at the Rallye Deutschland.
The Suzuki World Rally Team signed Gardemeister and new co-driver Tomi Tuominen for the 2008 season. He quickly showed pace, finishing seventh at the Swedish Rally in only their second event together. At Rally Japan, he set Suzuki's first-ever WRC stage fastest time and finished sixth overall behind team-mate PG Andersson — Suzuki's best individual points result of the year. When Suzuki announced its withdrawal from motorsport before the 2009 season, Gardemeister lost his works drive.
Gardemeister made occasional entries in the Intercontinental Rally Challenge in 2009 and 2010 with Astra Racing's Fiat Grande Punto Abarth S2000, retiring from both Monte Carlo editions from strong positions. He also returned to Rally Finland in 2010 in a Ford Fiesta S2000, finishing twelfth. In 2011, he contested the IRC full-time in a Škoda Fabia S2000 under his own TGS Worldwide OU banner, finishing inside the top ten on most rounds with a season-best sixth at Barum Rally Zlín, ending ninth in the standings. A serious back injury sustained at the Silk Way Rally in 2012 — two broken and one twisted vertebrae — ended his competitive career as a driver. After a nine-month recovery, Gardemeister redirected his focus to team management through TGS Worldwide, running Škoda Fabia S2000 and later R5 machinery for young talent. Among the drivers who progressed through TGS Worldwide are Teemu Suninen, Kalle Rovanperä, Juuso Nordgren, Eerik Pietarinen, and Pontus Tidemand.
Gardemeister represents a generation of Finnish rally drivers who built careers across manufacturer and privateer outfits in an era when several factory programs — SEAT, Škoda, Suzuki — came and went within single seasons. His 2005 Ford campaign remains his competitive peak, and his subsequent role nurturing future WRC stars through TGS Worldwide has extended his influence in Finnish rallying beyond his driving years.