The capital club announced on Wednesday night the 20-year-old, who won the Under-20 World Cup earlier this month, had signed a five-year deal with the Ligue 1 champions.
Digne said on the official PSG website: "To play for Paris St Germain, with these exceptional players, is a dream come true. I'm very happy.
"After the World Cup title in Turkey, I am having an incredible summer. I would like to thank the club for the confidence they have placed in me."
Digne made his Ligue 1 debut for Lille during the 2011/12 season and established himself in the first team last season.
PSG president Nasser Al-Khelaifi said the capital club had fought off interest from several clubs to land the rising star.
He said: "Lucas Digne, a rising star of French football and recent winner of the U20 World Cup, was the subject of transfer interest from a number of major clubs and has chosen Paris St Germain to continue his progression on the European stage.
"We are delighted to welcome this young French player into our squad."
Digne's arrival comes hot on the heels of that of Edinson Cavani, whose big-money move from Napoli on a five-year deal was completed yesterday.
And the Uruguayan striker has set his sights on forming a formidable strike partnership with Zlatan Ibrahimovic.
"Fantastic!" he said on www.psg.fr. "Ibra is a champion, a world-class player and to play alongside him will be a pleasure. "He's a winner, used to winning. It's a very positive thing and I hope to form a great attacking duo with him."
PSG were crowned French champions last season for the first time in 19 years and also reached the Champions League quarter-finals.