Digne, who will turn 20 on Saturday, became a first-team regular for Lille last season and featured in the Champions League for the Ligue 1 club.
Digne played for France during their under 20 World Cup winning campaign in Turkey earlier this month.
"We are delighted to welcome this young French player into our squad", Paris St Germain president Nasser Al-Khelaifi said on the club website.
Digne said: "To play for Paris St Germain, with these exceptional players, is a dream come true."
- Sports & Recreation