Hughes joins the south-coast club on a one-year deal after his contract with QPR came to an end.
Hyypia took over at Brighton from Oscar Garcia, who resigned from his post in May following their Championship play-off semi-final loss to Derby County.
And the former Bayer Leverkusen boss is confident that the experience of ex-Newcastle United, Aston Villa and Fulham man Hughes will be of value to his side as they look to mount another challenge for promotion to the Premier League.
"We wanted to bring another experienced defender, and Aaron fits the bill - having played at Premier League, Champions League and international level," Hyypia told Brighton's official 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.
"He has that experience I wanted to bring into the squad, which alongside our other senior players, will help our younger players continue to develop and progress in the first-team squad.
"Overall, we still have some work to do in terms of recruitment, and we are all working hard to do that. This is a good start and Aaron is a great addition."
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