Defender Haidara was released by Newcastle at the end of his contract.
The 25-year-old saw his contract at Newcastle expire last month after making just two appearances for the Toon's first team throughout the entire 2017-18 campaign.
A two-time France Under-21 international, Haidara failed to properly recover from a long-term knee injury that he suffered midway through his five-year spell at St. James' Park - joining The Toon from Nancy in January 2013.
Haidara confirmed a move to RC Lens on Instagram, thanking his new fans for the support they had shown him following a move to the French club. It sees Haidara return to his home country, signing a deal until 2020.
Haidara joined from Nancy and worked his way into the first team, he managed 54 appearances in all competitions, but only five of those came in the last two seasons.
The French defender will be looking to help Lens avoid relegation from Ligue 2, with the club finishing six points above the drop zone in 14th place last season.
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