The 20-year-old has joined the Seagulls on a season-long loan agreement after playing a starring role in the Championship last season for Albion's rivals Huddersfield Town.
He played 19 games and netted five goals to helping the Terriers secure promotion to the Premier League alongside Albion, via the play-offs, after joining in January.
But with Huddersfield also interested in bringing Brown back he has instead opted for the south coast - and is set to play tonight as Albion face their third warm-up match at Southend United.
Seagulls boss Chris Hughton said, "The natural progression for Izzy, having enjoyed such a successful season in the Championship last season, was to step up to the Premier League - and we are delighted he will be doing that with us, here at Brighton.
"He is a player with great potential and will bring a different dimension to our attacking options for the season ahead, alongside our existing strikers."
The England under-20 player also spent time on loan at Rotherham last season and has featured in the Premier League as a youngster with West Brom after coming through the club's academy, before joining Chelsea in 2013.
He counts a Premier League under-21 medal and FA Youth Cup double amongst his achievements as well as a being a UEFA Youth League champion.