Cavani, 26, finished top scorer in Serie A last season with 29 goals and successfully completed a medical with the Ligue 1 club before signing a five-year deal.
It is the latest big catch for Qatari-backed PSG who have spent more than 200 million euros in transfers over the past two years.
The move is the most expensive transfer in the history of French football.
The previous mark was set earlier this summer when newly-promoted Monaco paid Atletico Madrid 60m euros (£52m) to sign Falcao.
Cavani has spent three prolific seasons with Napoli having joined the club from Palermo in 2010, scoring 104 goals in 138 games for the southern Italian side.
The Uruguay international, who has 54 caps, could form one of the most formidable attacking pairs in Europe with Ibrahimovic.
The Swede led PSG to their first Ligue 1 title since 1994 last season by netting 30 goals, the first top-flight player to reach the mark in 20 years.
"Ibra is world class. It is a pleasure to play alongside him to try to win titles," Cavani said.
"I know many players in the team. El Pocho (Lavezzi), Pastore from Palermo, Diego Lugano from Uruguay," he added.
"I am familiar with Ligue 1, I like it and I am looking forward to playing here
"My message to the fans and the city is that I want to win and complete all of our objectives.
"I want to learn French. It goes beyond just needing it to play football. It will benefit me"
PSG president Nasser Al-Khelaifi said that the move did not mean the club was now looking to sell Ibrahimovic.
"Obviously we have bought Cavani to play alongside Ibrahimovic. The final decision is down to the coach," he said.
"The transfer of Edinson Cavani is further proof of the club's ability to attract the best players in the world," Al-Khelaifi added.
"The player was seduced by the club's sporting project and is delighted to be joining an ambitious side, impatient to take on new challenges."
- Sports & Recreation