Fellow Seagulls players Lewis Dunk and Shane Duffy have also made long-term commitments to the club, it was announced on Thursday.
Dunk, like Knockaert, has signed until 2022, while Duffy will stay at the Amex Stadium until 2021 having penned a four-year contract.
Frenchman Knockaert was a January 2016 arrival from Belgian side Standard Liege and hit 15 goals last campaign as Albion finished runners-up in the Sky Bet Championship.
Brighton boss Chris Hughton said: "Lewis, Shane and Anthony were key members of our promotion-winning side last season, and I fully expect them to be important members of the team once again this season
"They're relishing the step up to the new level and they each have the capability to perform and excel in the Premier League - and they have certainly earned these new deals with their performances on the pitch.
"I'm absolutely delighted that three key members of the squad have committed their futures to the Albion."
Dunk made his Brighton debut in 2011 and is their longest-serving current player, while fellow centre-back Duffy joined from Blackburn last summer.
Source : PA