Ferguson's new contract will now run until the summer of 2029.
The 19-year-old only signed an extension to his previous deal in April this year lasting until 2028.
Ferguson has scored five goals in eleven Premier League games this season, including a hat-trick against Newcastle United back in September.
Ferguson joined Brighton from Bohemians in January 2021 but his breakthrough season came in 2022/2023.
“Evan deserves this new contract and he has a very big future ahead of him,” Brighton head coach Roberto De Zerbi said.
Brighton technical director David Weir added: “Evan is a brilliant young talent and we are delighted for him.
“He’s shown his ability at club and international level, after breaking into the team at the start of the year, and we are looking forward to working with him and watching his continued progress.”
Ferguson has won eight caps and scored three goals for the Republic of Ireland national team.
