Albion have continued their transfer window blitz, beating off Championship and League One club interest to land the signing of Stockport County left-back Jim McNulty for a fee of £150,000.
The player originally turned down the move, earlier in January, after Albion chairman Dick Knight had agreed terms between the clubs.
However, after further talks in the past week the 23-year-old has signed a three-and-a-half-year deal with Albion, completed this morning, and will be available for tomorrow night's League One match with Peterborough United at Withdean.
McNulty said, "I wasn't looking to move away from Stockport County, I was happy there, but the persistence of both the Brighton chairman Dick Knight and manager Micky Adams eventually convinced me that this was the right move for me.
"It is an exciting move for me and with the brand new stadium only a couple of years away, Brighton are a club with obvious ambitions which match my own."
Micky Adams added, "Jim fits the criteria for a modern day player at this level. He's got good pace, a nice left foot and is a fantastic addition to the squad which I am trying to mould at the club."
The Liverpool-born full-back began his career as a trainee with Wrexham, and gained experience with Caernarfon Town in the Welsh League, before former Albion manager Brian Horton brought him back to the Football League at Macclesfield in 2006, before his switch to Stockport this time last year.
Chairman Knight added, "This is an exciting signing - and one which we have had to persevere with in the face of some serious competition.
"Jim first caught our eye with an outstanding performance against us at Stockport earlier in the season. Our scouts have watched him regularly since, which confirmed our interest in the player.
"He was one of our main targets this transfer window and I am delighted we have finally secured his services. He is a talented player who has lots of potential. I would like think he will be a mainstay of our defence for some years to come."