The midfielder has passed a medical and signed a two-year deal that has an option to extend his stay in southwestern France for another year.
He has been handed his favourite No 19 jersey, which he wore for both former side Hanoi FC and the national team.
“I have had medical tests at Pau Football Club. Everything is good. I have reached all requirements of health," Hai posted on his Facebook on June 29.
"The first important step is done. I am an official player of Pau FC from this moment. I am happy and proud.
"Thank you all, parents, family, supporters, media and all people who have been accompanying me on my journey. Let's fight!" he wrote.
On the club facebook fanpage, Pau FC posted: "Nguyen Quang Hai is here! Vietnam's international offensive midfielder (45 selections) joins Pau FC for the next two seasons. He will wear Pau FC's No 19. Welcome, Quang Hai!"
A short video introducing the Vietnamese player is also available on the page.
The 25-year-old, who also received offers from clubs in Thailand, Japan, Spain and other countries, will have about a month to make himself familiar with his new environment and earn a place in the starting 11.
Pau FC's Coach Didier Tholot praised Hai's abilities but has not revealed where he will utilise them in the favoured 4-4-2 formation of the club.
Pau FC returned to training on June 24. Hai will join his new teammates in Saint-Paul-les-Dax on July 3, ahead of pre-season matches against Ligue 2 champions Toulouse on July 8, Angouleme on July 15 and Niort on July 23.
They will then have a week's rest before beginning their Ligue 2 season on July 30 away to Guingamp.
Pau FC were established in 1904. Last season they finished 10th out of 20 clubs in Ligue 2.
Showing Quang Hai's popularity among Vietnamese football fanatics, Pau FC's Facebook page received hundreds of thousands of likes and comments since the news broke that he would be joining the side.
At 11.30am on June 29, the club has had more than 155,600 likes and 201,000 followers, nearly 10 times the numbers of the week before.
Ligue 1, France's premier league, also posted a picture of Hai in Pau's jersey along with Vietnam's national flag on their fan page, which has almost 7.5 million followers. They welcomed Hai in both English and Vietnamese.
While the Ligue 1 page usually posts transfer news from their own league, this is the first time such a deal from Ligue 2 has been highlighted.
Hai is the eighth Vietnamese player to play abroad. While Vietnam has been represented in China, Portugal, Japan, the Republic of Korea and the Netherlands, most of these overseas ventures proved unsuccessfully. Quang Hai will be hoping to buck that trend over the coming years./.
