The 19-year-old joins the Whites from Ligue 2 side Lorient on a season-long loan deal.
Meslier made his senior debut at Lorient last August in a 1-0 victory over Valenciennes in the Coupe de la Ligue.
In total he made 30 appearances for the French side during the 2018/19 campaign in all competitions, recording 11 clean sheets.
He has also won caps at both Under-18 and Under-19 level with France.
Subject to international clearance, Meslier could be included in the Leeds squad for the first time in Saturday’s clash with Nottingham Forest at Elland Road.