Jarrett has rarely figured for the Lilywhites since his switch to Deepdale from Norwich City in 2006 and has been loaned out several times.
He has made just three appearances so far this season and is no longer wanted at his club.
Micky Adams, the Seagulls manager, has been quick to move for the 29-year-old, who is expected to sign for the Seagulls until the end of the season.
Adams told his club's official website: "I'm sure Jason will prove an important addition. He can add another dimension to our midfield while bringing some experience to the squad."
Jarrett has been on loan at Wrexham, Bury, Wigan, Stoke, Plymouth, Hull, Leicester and Queens Park Rangers during his time at Preston.
Brighton have also taken former player Seb Carole on trial. The winger left the Withdean Stadium for Leeds in 2006 but was released by United last summer. He has spent time at Darlington and training with Bradford City.