The 24-year-old wide-man, who began his career with Olympique Lyonnais, becomes the French champions' third signing of the summer
Montpellier have announced the capture of winger Anthony Mounier from Nice for a reported fee of €3.25 million.
The 24-year-old has put pen to paper on a four-year deal, and joins Daniel Congre and Gaetan Charbonnier as the club's early summer arrivals.
Lyon and St Etienne both expressed an interest in acquiring Mounier's services, but La Paillade beat off the competition to get their man.
The Ligue 1 champions have already lost last season's top-scorer Olivier Giroud to Arsenal, and are moving quickly to swell their ranks ahead of their first-ever Champions League campaign.
Montpellier were last season's surprise package in the French top flight, clinching their first-ever league title on the final day of the season.