The Norwegian has joined until the end of the season.
"With Shane out for a minimum of six weeks, alongside Lewis Dunk, Uwe Huenemeier and Fikayo Tomori, Vegard gives us another central defensive option for the run-in."
"Vegard has played the majority of his career for Molde, one of the top clubs in Norway, and has an excellent pedigree having also played in the Champions League, Europa League and 33 times for his country.
Manager Chris Hughton commented, "Vegard is a player the club had been aware of for sometime, and with the absence of Shane Duffy and Connor Goldson, we felt it was important to take this opportunity to add to our defensive options.
Subject to international clearance, Forren, who has 33 caps for Norway, would be eligible for this Friday night's visit of Derby County.
The 29-year-old central defender passed a medical at the American Express Elite Football Performance Centre earlier today and completed the paperwork.
Brighton & Hove Albion have signed Norwegian international defender Vegard Forren until the end of the season.
LATEST NEWS FROM SEAGULLS.CO.UK
REPORT: ROTHERHAM 0 ALBION 2
- U23 REPORT: ALBION 4 MIDDLESBROUGH 2
- MURRAY'S POSITIVE PERSPECTIVE
- 2017-18 SEASON-TICKET RENEWAL INFORMATION
- KNOCKAERT SIGNS CONTRACT EXTENSION
Aside from a six-month spell at Southampton, left-sided defender Forren has spent the past ten years with Molde, winning three championships and two domestic cups.
He turned down a new contract at the club last season, and left the club when the domestic season ended in November.
Recently he had been pre-season training with Norwegian side Rosenborg.
Tweets by @OfficialBHAFC