The 20-year-old versatile forward moved to the Chelsea academy from West Bromwich Albion in the summer of 2013 as an exciting prospect for the future.
He won the Premier U21 League and FA Youth Cup double in the 2013-2014 season and was handed his first-team debut by Jose Mourinho during a 3-0 defeat to the Baggies in May 2015.
The Under-20 England international continued his development at Vitesse Arnhem during the 2015-2016 campaign and had two different loan spells at Rotherham United and Huddersfield last season, helping the Terriers to secure a promotion to the Premier League while scoring five goals in 21 appearances.
Antonio Conte's side have now opted to send him on loan to Brighton in order to give him a experience in the Premier League.
Nevertheless, he has committed his long-term future to Stamford Bridge with a new four-year deal - an indication that he remains very much in the long-term plans of the Premier League champions.
"Izzy Brown has today signed a new contract until 2021 and joined Premier League newcomers Brighton and Hove Albion on loan until the end of the season," Chelsea have confirmed.
Brown becomes Brighton's sixth signing of the summer following the arrivals of Pascal Gross, Josh Kerr, Mathew Ryan, Markus Suttner and Mathias Normann.
Manager Chris Hughton has welcomed his arrival, hoping the Chelsea starlet could help the Seagulls to establish themselves in England's top-flight.
"We are delighted that we've been able to bring Mathias to the club," Hughton told Brighton's official website.
"He is a talented and versatile young player, who already has good experience playing regular senior football in Norway. We are looking forward to welcoming him into the club and his longer-term plan will be to break into the first-team group."