After saying goodbye to his Barca teammates, Neymar has travelled to Porto - where PSG sporting director Antero Henrique had worked until recently - by private jet from Barcelona to complete his medical. He was surrounded by his entourage, including his father and agent Neymar Sr.
At $263m, Neymar's buyout clause would more than double the current transfer record set by Paul Pogba's $111m move to Manchester United last year.
Earlier, Barcelona ended weeks of speculation by publicly confirming for the first time the 25-year-old's wish to leave after four years at the Camp Nou.
"Neymar Jr, accompanied by his father and representative, communicated to FC Barcelona this morning his decision to leave the club," Barcelona said in a statement.
"The club have informed them that the buyout clause in his contract, that from July 1 is 222 million euros ($260m), must be paid in full."
Neymar has been tempted to Paris by an astronomical offer that would reportedly see his wages tripled to 30 million euros ($35.6m) a year after tax.
However, on the field he also faces the challenge of stepping out of the shadow of five-time World Player of the Year Lionel Messi to try and prove himself as the world's best.
"It was a huge pleasure having shared all those years with you, my friend @neymarjr," Messi posted on Instagram alongside a montage displaying some of the pair's finest moments together.
"I wish you lots of luck in this new stage in your life. See you soon tkm," he added. "Tkm" stands for "te quiero mucho" (I love you loads).
"Thanks brother. I will miss you man," Neymar replied.
Winning the Champions League for a first time is the dream driving PSG's owners Oryx Qatar Sports Investments (QSI) to fund a deal that could herald the start of a new era at the elite level of European football.
Since QSI's takeover in 2011, PSG have failed to make it beyond the quarter-final stage in recent seasons - most notably blowing a 4-0 first leg lead to lose 6-1 to a Neymar-inspired Barcelona in the last 16 of last season's competition in March.
Presuming both clubs don't come to a late agreement, the buyout clause would have to be paid to Barcelona via Spain's La Liga to free the player from the contract he signed last year and runs until 2021.
However, La Liga President Javier Tebas has threatened not to accept PSG's money over what he perceives as a failure on the French side's part to comply with UEFA's Financial Fair Play rules (FFP).
Clubs can be sanctioned by UEFA for making a loss of more than 30 million euros over a three-year period.
"We will not accept this money from a club like PSG," Tebas told Madrid sports daily AS on Wednesday. "Especially when this club is infringing rules and laws."
Source: News agencies