Dunk, 28, had been heavily linked with a move to Chelsea but the club took many by surprise as they announced the deal on Friday afternoon.
“I’m delighted to have signed a new contract,” Dunk said. “The aim now is to build on a record Premier League season and help the club continue its recent progress over the next five years.”
Dunk is Brighton's player of the season and has been at the club for 10 years.
Here's how social media reacted.
@AlbionAnalytics: Lewis Dunk is the fourth longest serving player to any Premier League team. His tenure at Brighton currently stands at 10 years, 1 month and 21 days - his contract extension lasts until the end of the 2024/25 season.
@DJDixon90: I always wanted the best for Dunky which is why I would have loved to seen him play champions league football and compete for titles; the fact he’s staying until retirement, says a lot about him as a person. What a man. #BHAFC
@CaddyWooldridge: Dunk and White CB partnership next season. #BHAFC looking solid.
@SeagullsCentral: Never underestimate how important Lewis Dunk is to #BHAFC. So integral to keeping us up the last 3 years. This contract shows that there probably never was any genuine attempt from Chelsea to get him. Looking forward to another 5 years of Dunky!
@GeddesChris: He’ll always be one of our own! He should be massively applauded for his loyalty. I’m sure he could have ‘cashed in’ with a move to one of the so-called big clubs! #bhafc
@TogetherBHA: He knows that staying with us hurts his England career due to the big club bias, he knows he could walk into almost any PL clubs backline and yet he persists. Truly a King, a Captain and one of our own. Take a bow Lewis Dunk #BHAFC
@TheRedSeagull92: Absolutely delighted with that news! Lewis is vital for us #BHAFC
@stuhenry16: New 5 year deal for Dunk. Ben White in the training pics today. Lallana just looking superb. Happy Friday Brighton fans #BHAFC
@WhaleyStatic: Wow!!!!!!! Did not expect this but I love it #BHAFC
@barney_furlong: Mr Brighton and hove Albion stays on! @lewisdunk #BHAFC
@BHAFC_NEWS: Wonder what’s the highest number of contract extensions at one club? Because Dunk must be close