The Seagulls say they beat off competition from Premier League clubs to land March, who was once on the books at Chelsea.
Director of football Martin Hinshelwood told the club website: "He's been recommended to us a couple of times and we've been following him for a while now, in which time he has impressed us all.
"It got to the stage where a few other clubs became very keen on him so we've completed the deal and we're looking forward to working with him.
"It's a good move for him but also the way the manager wants to play will hopefully be good for him in the future.
"He's bright and lively on the ball and he's got very good passing ability."