De Cuyper, 24, helped Brugge win the Belgian Pro League in 2023-24, and the Belgian Cup last season. He made his Belgium debut in June 2024, and has earned 10 international caps, scoring three goals.
"He has a great reputation for creativity and has shown his ability across different positions, although we primarily see him challenging for a left-back spot with us," Brighton coach Fabian Huerzeler said in a statement.
Brighton begin their league campaign at home to Fulham on August 16th.