No financial details were given.
The Sydney-born 25-year-old will join in July, subject to international clearance, after a break following the Confederations Cup which starts in Russia on Saturday.
"I'm delighted that we've been able to attract Mathew to the club, and he will certainly be an excellent addition to the squad in time for our first season in the Premier League," manager Chris Hughton told the club website.
"For somebody of Mathew's age, he has very good experience, having played in the top divisions in Australia, Belgium and Spain. He has also competed in European competition and made a number of appearances at international level."
Ryan moved to Club Bruges in Belgium in 2013, making more than 100 appearances.
He played for the Socceroos in the 2014 World Cup in Brazil and signed a six-year deal with Spanish side Valencia in 2015 but made only 10 appearances. Ryan was loaned to Belgian side KRC Genk towards the end of last season.
(Reporting by Alan Baldwin, editing by Ed Osmond)
Share
