Hughes, 34, joins the Seagulls for free on a one-year contract after leaving Queens Park Rangers at the end of last season.
"We wanted to bring another experienced defender, and Aaron fits the bill having played at Premier League, Champions League and international level," Hyypia told the club website.
"I have played against Aaron a few times during my time at Liverpool and also for Finland, and I know his qualities and what he will give us.
"He has a very good footballing pedigree, is an intelligent player, and he has a great mentality and good approach to the game."
Hughes made 24 Premier League appearances last season for both QPR and Fulham, and has 90 international caps with Northern Ireland.