The deal, which has the option of a third year, is subject to a medical.
The Argentina captain, 34, left Barca - the only club he has played for - as they could not afford a new deal under La Liga's financial fair play rules.
A PSG news conference will take place in the auditorium of the Parc des Princes on Wednesday at 10:00 BST.
Mauricio Pochettino's PSG finished second to Lille in Ligue 1 last season.
"It's all been confirmed. Lionel Messi is going to be a PSG player," Balague said on BBC Radio 5 Live. "That's it, it's done. It's happened in the last few minutes.
"At the moment there are as much police as there are fans [at the stadium]. That's going to change soon. There's eight cameras here, again that's going to change. It seems like it is a two-year deal, plus one.
"His idea was to do it at Barcelona but it's going to be PSG. Then if he feels OK he will stay one more year maybe. But in any case his aim is to be at PSG and then to do well in the Qatar World Cup."
Messi and his family were pictured at Barcelona's El Prat airport on Tuesday afternoon after news of the deal emerged.
When asked by reporters whether his son would be joining PSG, Jorge Messi answered "yes".
Considered one of the greatest players of all time, Messi scored a record 672 goals in 778 games for Barca, the club he joined as a 13-year-old.
He won the Ballon d'Or a record six times and lifted 35 trophies with the Catalan club.
The signing of Messi - who would be reunited with former Barca team-mate Neymar at the Parc des Princes - is one of the most noteworthy captures in football's history.
He will play in a front three alongside the two most expensive players of all time - Neymar and Kylian Mbappe.