France-born Sankhare, who started his career with Paris Saint-Germain, spent the past three seasons with Guingamp and scored six goals last year to help the Brittany club in their battle against relegation.
"I'm very happy to be here, I received an excellent welcome. I'm looking forward to meeting my new team-mates and above all playing. For an ambitious player like me, (Lille) is the perfect club," Sankhare told the club's official website.
Lille recovered from a disastrous start last season, which cost two-time Africa Cup of Nations winner Herve Renard his job as coach, to finish fifth in the table and qualify for the Europa League.