Stijn Devolder (born 29 August 1979) is a Belgian former professional road bicycle racer, who competed professionally for Vlaanderen–T Interim (2002–2003), Discovery Channel (2004–2007), Quick-Step (2008–2010), Vacansoleil–DCM (2011–2012), Trek–Segafredo (2013–2016), Vérandas Willems–Crelan (2017–2018) and Corendon–Circus (2019).

Primarily a classics rider but also adept in individual time trials, Devolder took a total of eighteen victories during his professional career, including three wins in the Belgian National Road Race Championships (2007, 2010 and 2013), two wins in the Belgian National Time Trial Championships (2008 and 2010), and is one of seven riders (as of 2026) to win consecutive editions of the Tour of Flanders, winning in both 2008 and 2009.

Born in Kortrijk, West Flanders, Devolder won the junior Tour of Flanders in both 1996 and 1997, and the junior Belgian National Road Race Championships in 1997. He joined the under-23 development team run by Eddy Merckx in 1999, taking eight victories over three seasons – including consecutive successes at the Grand Prix de Waregem in 2000 and 2001. Towards the end of the 2001 season, Devolder rode for the Mapei–Quick-Step team as a stagiaire, forming part of a breakaway group during the GP Ouest-France.

Devolder turned professional for the 2002 season with the Vlaanderen–T Interim team. In his first season with the team, Devolder finished second in the GP de Fayt-le-Franc and Zellik–Galmaarden one-day races. The following year, Devolder finished third in the E3 Prijs Vlaanderen – one of the cobbled classics – having attacked as part of a three-rider move inside the final 30 kilometres (19 miles) of the race.

Devolder joined U.S. Postal Service for the 2004 season, and in his second start with the team, finished third in the Tour du Haut Var from a group sprint of four riders. He finished sixth in the Three Days of De Panne in the spring, before taking his first professional victory at the Four Days of Dunkirk, taking a solo win on the fourth stage into Boulogne-sur-Mer. The following year, he won the general classification at the Three Days of De Panne, overturning a four-second deficit to Alessandro Ballan on the final stage, a 13.7-kilometre (8.5-mile) individual time trial around De Panne. He also contested a Grand Tour for the first time, riding for the now-renamed Discovery Channel team at the Vuelta a España. Having been unable to defend his title at the Three Days of De Panne, Devolder took his only victory of the 2006 season in an individual time trial stage at the Tour of Belgium – as part of a Discovery Channel 1–2–3 in Buggenhout. He rode the Vuelta a España for the second year in a row, recording his best Grand Tour result with eleventh place overall, finishing just over a minute behind the top ten placings.

In 2007, Devolder won the final individual time trial stage at the Three Days of De Panne, before he finished third overall at the Tour de Suisse, having advanced from seventh prior to the final stage, an individual time trial around Bern. The following week, Devolder won his first senior national title as he won the Belgian National Road Race Championships in Ronse, following a 10-kilometre (6.2-mile) solo move. He wore the jersey for the first time at the Tour of Austria where, after a fourth-place stage finish at the Kitzbüheler Horn on stage three, Devolder took the race lead when he won the penultimate stage – a 25-kilometre (16-mile) individual time trial in Podersdorf am See – by almost a minute. He ultimately won the race by more than a minute from the next closest competitor, Thomas Rohregger. At the Vuelta a España, Devolder finished third on the fourth and eighth stages, moving into the race leader's jersey as a result; he ultimately ceded the lead after one day, losing five minutes to Denis Menchov on the summit finish at the Cerler ski station. Devolder ultimately abandoned the race as he failed to start stage 19, having lost 27 minutes on the previous stage due to a crash.

Devolder joined Quick-Step for the 2008 season, following the disbanding of the Discovery Channel team. He took his first victories with the team at the Volta ao Algarve; he won the fourth stage individual time trial by twenty-two seconds to take the overall race lead, which he held to the finish the following day. Moving into the cobbled classics, Devolder was expected to be a key helper for teammate Tom Boonen at the Tour of Flanders, but he attacked with 25 kilometres (16 miles) remaining and ultimately soloed to victory in Meerbeke. He was designated the same role at Paris–Roubaix, and he finished in seventh place as Boonen won the race. Following a break from racing, Devolder won the general classification in his next start at the Tour of Belgium; he finished second to Greg Van Avermaet on stage three, before winning the stage four individual time trial to take the race lead, which he held to the end of the race along with the mountains classification. He ran as high as fourth overall at the Tour de Suisse, before making his first start at the Tour de France, where he led the Quick-Step team. Seventh overall after nine stages, Devolder cracked on stage ten and lost twelve minutes to the main general classification contenders, before abandoning on stage fifteen. Aside from a fourth-place finish at the Eneco Tour, Devolder's best results over the remainder of the season came in individual time trials as he won his first Belgian National Time Trial Championships in Mouscron, and he finished sixth in the time trial at the UCI Road World Championships in Italy.

Having extended his contract with the team for a further two years, Devolder recorded top-ten placings in the early part of the 2009 season at Dwars door Vlaanderen and E3 Prijs Vlaanderen – finishing fifth and sixth respectively – after attacking moves in both races. He then repeated his victory at the Tour of Flanders; having bridged up to the lead group on the ascent of the Valkenberg with Boonen and Filippo Pozzato, Devolder attacked on the penultimate hill, the Muur van Geraardsbergen, and ultimately won the race in Meerbeke by approximately one minute. He took no further victories over the remainder of the year, his best result being a fourth-place finish at the Belgian National Time Trial Championships in Saint-Ghislain, following a crash.