De Mévius entered the World Rally Championship racing in the Group N category with a Mazda 323. Group N competition, which used near-standard production cars with limited modifications, was a common entry point for privateers looking to establish themselves in the WRC paddock without factory support. An unsuccessful period of Group A racing in 1990 did not elevate his profile among the sport's leading contenders, and he was not widely regarded as a frontline talent during this phase of his career.
In 1993 De Mévius secured a more settled place as a privateer in the Group A WRC category. Running without works backing, he competed on his own terms against factory machinery across a variety of rally surfaces. He recorded a series of finishes within the top six on gravel events, demonstrating consistent pace on stages where privateers could occasionally match the cars if not the budgets of manufacturer teams.
His best WRC result came at the 1998 Network Q Rally of Great Britain, where he finished fourth for the Privateer Belgacom Turbo Team in a Subaru Impreza. The Network Q Rally, held on the mixed-surface and often wet roads of Wales and Yorkshire, was an event where privateers could sometimes close the gap to the frontrunners, and De Mévius made the most of the conditions to secure a result that stood as his career high in the WRC.
After retiring from WRC competition, De Mévius moved to rally raid, a discipline that suited drivers with the endurance and navigational demands of multi-day desert racing rather than the pure pace required in traditional rallying. He became a regular contender at the Paris–Dakar Rally, competing for the manufacturer Nissan team and later for BMW X-Raid, one of the leading operations in the car category.
During the 2000 Paris–Dakar–Cairo Rally, running near the front of the field for Nissan, De Mévius was caught up in a freak incident in which four cars competing near the top of the classification all arrived simultaneously at a collapsed dune. The convergence resulted in multiple collisions and De Mévius was among the competitors to sustain back injuries.
The 2003 Dakar Rally brought De Mévius his closest approach to the overall podium. Running as high as third in the BMW, he was forced out of contention when an impact with a rock damaged the steering on his car. In 2004, again driving for BMW and again in early podium contention, a significant engine failure compounded by a rollover dropped him to an eighth-place finish. His 2005 campaign brought him back to the Nissan France team, now driving an older-specification pick-up, but ended in retirement following a serious crash that required him to be airlifted to hospital.
De Mévius's sons, Ghislain De Mévius and Guillaume De Mévius, both became rally drivers, continuing the family's connection to the sport into a second generation.