Laussucq (34) has three caps for France and played in the Top 14 and Heineken Cup with Castres Olympique last season. He is also a two-time French Championship winner from his spell with Stade Francais.
He made an appearance as a second-half replacement for Leicester Tigers in Saturday's pre-season fixture against Nottingham at Welford Road and will go straight into the pre-season training programme with his new team-mates.
Tigers acting head coach Richard Cockerill said: "It is no secret that we have been looking for some experienced competition for the scrum-half spot with Harry Ellis and Scott Bemand sidelined by injury for a decent length of time. Christophe certainly has the experience gained at the top level in France.
"He did a decent job on Saturday after coming in at short notice and now we are looking for him to join the pre-season work, settle in quickly and join Frank Murphy and Ben Youngs in the frame for that number nine shirt."