A deal had already been reached with Sao Paulo for the 20-year-old attacking midfielder, and the transfer was completed in Qatar today with the youngster putting pen to paper on a four-and-a-half year contract.
Lucas joins a club which invested heavily in players last summer following the takeover by wealthy new owners Qatar Investment Authority.
And the youngster is hoping he can quickly make his mark as PSG look to win their first Ligue 1 title since the 1993/94 season.
"Choosing PSG is a challenge for me," he said in a press conference.
"They have a long history with Brazilian players and I hope I can add a new chapter to that story and please the fans.
"Everyone expects a lot from me but I have a lot of confidence.
"I'm glad to know (coach) Carlo Ancelotti is counting on me. I don't feel the pressure.
"I'll try to do my best and give my all for the team. I'm here to offer my assistance."
Lucas will take part in his first training session with his new team-mates later on Tuesday.