Striker Barnes scored his first league goals of the season as Brighton clinched their first home win since mid-September before a crowd of 27,912 at the Amex Stadium.
Brighton had a scare early on when Irish midfielder Alan Judge drove wide from the edge of the area following a good ball in from skipper Scott Dann.
Blackburn midfielder Tom Cairney later had a shot charged down before Rovers defender Jason Lowe saw a deflected shot go just wide.
The Seagulls struggled to make much of an impact until on-loan Cardiff winger Craig Conway forced former Derby keeper Jake Kean to parry his fierce shot breaking in from the right in the 20th minute.
Rovers players Cairney and Todd Kane both needed treatment following a collision inside their own penalty box when Stephen Ward attempted to get around the back of the visitors rearguard.
Barnes wasted a glorious opportunity to put the Seagulls ahead on 33 minutes when he blazed wastefully over after breaking clean through following a mistake by Lowe.
But Barnes kept his cool only two minutes later to put his side ahead with his first league goal of the season from the penalty spot.
Barnes gave keeper Kean no chance with a sweetly struck spot kick after substitute Dickson Etuhu brought down Conway.
Spanish midfielder David Lopez put a free kick from just outside the area over for Brighton but it was Rovers who finished the half on top with both Jordan Rhodes and Dann going close.
Rhodes should have hit the target when heading wide at the far post from a Joshua King cross, and then Seagulls keeper Tomasz Kuszczak expertly tipped over Dann's goal-bound header after Cairney's free kick.
Kuszczak did well again moments after the break by pushing a low drive from King round the post.
But Brighton were not having it all their own way and both King and Cairney had shots saved by the alert Kuszczak.
Young midfielder Forster-Caskey eased the Seagulls nerves, however, by doubling their advantage on 56 minutes by heading in a Conway cross.
Blackburn continued to seek a way back into the game and substitute David Dunn shot narrowly wide before a firm header from Tommy Spurr came back off the crossbar.
Barnes struck again to settle the outcome from close range 12 minutes from time from close range after Kean could only parry a goal-bound effort from Andrew Crofts.