By SABC Sport
26th August 2024
The 23-year-old joins Albion for a reported ã25million, subject to international clearance.
O'Riley featured more than 100 times for the Hoops over two-and-a-half years, scoring 27 goals and helping Celtic win the Scottish Premiership on three occasions.
Brighton boss Fabian Hurzeler said: "He plays a very specialist position. He is very good at occupying and attacking the right space and likes making deep runs, knowing when to attack at the right time.
"He enjoys getting forward and attacking the opponent's penalty area, but he also has a good defensive instinct. That balance makes him special.
"He is a great character, and has a good ambition to succeed and that's something which is very important for us."