The 21-year-old initially arrived at Elland Road from French side Lorient in the summer of 2019 on loan and made the move permanent last summer after Leeds United gained promotion to the Premier League.
Meslier played 35 times in the top flight last season, keeping 11 clean sheets as Marcelo Bielsa’s men finished in ninth position on their return to the Premier League after a 16-year hiatus.
Meslier said: "I'm so proud. I'm very happy to sign a new deal with Leeds, a big club, so it was natural to sign and I have no doubts.
"I have the chance to play in the Premier League at 21, which is not a given for everyone and I feel very happy to play every weekend against big teams.
"Last season I discovered the Premier League, I was young for a goalkeeper, so this season I have to confirm the challenge and take the opportunity the club has given me.
"I will give the maximum of myself and keep working every day with the goalkeeper coaches, it's an important season for me and the rest of the team too.
"We work hard every day with Marcelo to try and get the best out of ourselves, we were not surprised to finish ninth last season, but we know this season will be difficult because the teams know us now, so we have to work more to try and have another good season.
"This club is unbelievable, the stadium is full all of the time and you feel the atmosphere of the fans and we play football everybody likes.
"I can't wait to play in the Premier League with Elland Road full."
Leeds will begin their 2021/2022 Premier League campaign away at Manchester United on Saturday.
