After starting his career in 1986 in the lower divisions of the French leagues, Leboeuf moved to Laval in 1988. In 1991, he moved to Strasbourg and played there until 1996, when he made a switch to English club Chelsea for £2.5m.
For France, Leboeuf was capped 50 times, scoring four goals. Although he was mainly a substitiute in the 1998 World Cup, he stepped in for red cardedLaurent Blanc to play in the final, a 3–0 win against Brazil, a match in which he famously man-marked Ronaldo. In the final Ronaldo only was able to do a couple of his trademark runs thanks to an almost flawless defensive performance by Leboeuf.
A highly cultured centre back Leboeuf was noted for his long range passing ability and also for his consistent penalty-taking throughout his career. He took more than 20 penalties for Chelsea, missing just 3 times: against Leicester, Feyenoord and Blackburn.