Masina has penned a five-year contract with the Hornets.
"I am so happy to be here and I have come here to improve myself, to better my English and my professional life," he told the Watford website.
“I think the Watford staff are top staff and can help me to improve and become a new player.
“My thinking is to improve myself in any way possible. For me, that is the most important thing."
Masina is well aware of the nature of English football and the qualities he feels he possesses certainly lend themselves to the Premier League.
“I've followed the Premier League since two or three years ago because I think it is my style of football, and I think one day it can help me become better," he said.
“I am a left-back. I like to run, to fight and to play with the ball because the ball for me is important. I am physical, but this season I learned to use my body better."