The 28-year-old put pen to paper on a deal that will keep him at the Amex Stadium until the end of the 2019/20 season.
Baldock played an integral role in the Seagulls' promotion-winning campaign, scoring 12 goals last season as Brighton secured Premier League status for the first time in the club's history.
"As soon as the club made noises that they wanted to extend my contract it was always in my head that this is where I want to be," Baldock told the club's official website.
"Last season was probably the pinnacle of my career, and I hope now we can establish ourselves in the Premier League and continue to improve together."
Manager Chris Hughton added: "We are delighted that Sam has agreed a new deal with us
He has been a key member of the squad since he arrived at the club and this new contract is recognition of his contribution over the last couple of seasons.
"He's also a great professional and a good character in the dressing room, so we are pleased he will be with us for the next few seasons."
Baldock has made 88 appearances for Brighton following his move in the summer of 2014, scoring 20 times
He began his career at MK Dons before ending his six-year stint to move to West Ham in 2011
The former England-Under 20 international spent one season with the Hammers before moving to Bristol City
Source : PA