Saelens began his motorsport career in 1986 in karting where he was active until 1993. After he had taken part in the Belgian Touring Car Championship in 1993, he moved in 1994 to Formula racing and immediately became third in the Benelux Formula Renault. In 1995 he moved into the European Formula Renault. After he had finished the first season in ninth place, he was a year later behind Enrique Bernoldi runner-up. He also took part in some races in the French Formula Renault, which he finished in ninth place overall, in part.
In 1997, Saelens to ASM F3 in the French Formula 3 Championship. With two victories, he finished the season in third place in the overall standings. In 1998 he completed his second season in the French Formula 3 Championship for ASM F3. The Belgian chose 6 of 11 races for themselves and won the league title before Franck Montagny. Saelens was the first non - Frenchman to have won the French Formula 3 Championship. In addition, the racers won the Formula 3 Masters at Zandvoort.
In 1999 he moved into the international Formula 3000 championship and was first appointed to WRT Fina. After he failed to qualify for the first three races, he moved to Supernova Racing, where he replaced Ricardo Maurício. Saelens finished equal to the first race for his new team in third place on the podium. At the end of the season he finished, while his teammate Jason Watt became runner-up, the ninth overall. In 2000 he stayed with Supernova Racing and received with Nicolas Minassian a new teammates. As in the previous year was his teammate runner-up. Saelens finished with three third places for best results the seventh place overall.
In 2001 the Belgians to the Italian team European Minardi F3000. His team-mate Andrea Piccini he had this season in the handle, but podium finishes him were denied. After he had to miss two races through injury, he finished at the end of the season tenth overall. Parallel to his involvement in Formula 3000 Saelens started in the 2001 season for Team Rosberg in the DTM and was 21st in the overall standings. In 2002, the Belgians started in the first five races of the 3000 Formula for European Minardi F3000. He came only once to the finish and ended the season in 24th place overall. He also completed Formula 1 testing for the Formula 1 team, Minardi.
2003 left Saelens formula racing and joined the American Le Mans Series. With five podium finishes he finished the season in sixth place in the championship. He also took part in the 24 - hour race at Le Mans. In 2004 he moved into the GT sports and joined in the Porsche Supercup. After he had become in his first season in sixth, he scored in 2005 with three wins third overall, which represents his best finish in this series. Saelens remained three more seasons in the Porsche Supercup and in 2005 with his last win fifth in the overall standings. In 2007, he finished sixth and 2008 the twelfth overall.
Since 2009, Saelens is no longer active as a racing driver.