The 24-year-old opener has been a pillar of strength at Hove in recent years; teenager Dan Ibrahim has also extended his deal
Sussex captain Tom Haines has signed a contract extension at Hove after spending the winter with England Lions.
The 24-year-old made a century against Sri Lanka A and 82 against England in a warmup fixture ahead of their Test series win over Pakistan.
Haines has been a shining light in recent years for the county, leading a group of youngsters into senior roles. He ended last season with two centuries on the same afternoon in a remarkable draw against Glamorgan.
His new deal will see him remain at the county until the end of the 2025 season, with teenage allrounder Danial Ibrahim also extending his deal by the same timeframe.
"I'm really happy to have signed a new contract my home club," said Haines. "The next period looks really promising and I look forward to playing a part in that. The season coming up looks an exciting one, with more of a balance of youth and experience and we are all determined to win more games of cricket and push to win trophies."
Paul Farbrace, the county's new head coach, described him as "an outstanding batter in county cricket".
He added: "There is no doubt his name will be spoken about as an England opening in the near future."
Danial Ibrahim has also extended his contract by three years (Mike Hewitt/Getty Images)
Haines has been tipped by many – along with opening partner Ali Orr – to push for higher honours in the next few seasons, so his commitment to Sussex, particularly after a run of just two red-ball wins in the last two seasons, is a major boost.
Much is also expected of Ibrahim, the youngest player to make a County Championship half century. He made his debut at 16 and has since made 12 first-class appearances for Sussex, reaching three figures for the first time in the same draw with Glamorgan, before wintering with England Under-19s in Australia.
"I'd like to say a big thank you to my mum and dad who have continued to both play a big part in my career so far," he said.
Farbrace called him "without a doubt one of the most exciting young talents in English cricket".