Previous manager Gus Poyet was sacked over the weekend - something he is appealing, but the club have wasted little time in creating what they describe as a 'newly created' role for Garcia to take up.
40-year-old Garcia quit as Maccabi Tel Aviv boss last month, and takes charge of a side which finished fourth in the Championship last season - before losing out in the play-offs to Crystal Palace.
"I am delighted to have the opportunity to work in English football for the first time," Garcia told the club's website.
"Brighton & Hove Albion is one of the most exciting and progressive clubs in the country."
Chairman Tony Bloom added: "We are delighted to have Oscar here to help us prepare for the new season and plan what promises to be another exciting campaign for the club."
Meanwhile, following on from Poyet's departure the club have confirmed that his assistant boss Mauricio Taricco has left the club by mutual consent.