Lascelles skippered the Magpies to a top-ten finish last term, having worn the armband during the 2016/17 season as United won the Sky Bet Championship title.
He was rewarded for his performances at the heart of Rafa Benítez's defence with a new deal last year, but has now agreed an improved and extended contract with the United boss today describing the centre-back as "the future of the club."
Born in Derby, the 24-year-old joined Newcastle from Nottingham Forest in 2014. He has made 112 appearances for United, scoring eight goals.
Speaking about his new deal, Lascelles told NUFC TV: "I'm over the moon - it's great news to be tied down to Newcastle for a long time. It's pretty much all I ever wanted: playing in the Premier League in front of amazing fans.
"I think now as players, we just need to give the fans what they deserve. We need to put in the performances and make it even more special.
"Since I've been here, everything's been really positive and now I need to get my head down and get this team higher up the league."
Manager Benítez said: "I'm really pleased to see Jamaal sign a contract extension. He's the future of the club and someone who really cares.
"The fans are looking for players who care about the team and the club, and he is one of these players.
"He's still a young player, still a young captain and still a young centre-back, so we're talking about a player who has a great future, because normally you consider the peak of a centre-back could be between 28 years old and 30 years old, so still he has plenty of room for improvement.
"He's keen to learn and he's working hard, trying to be a better player every day, so it is good news for the club."
Lee Charnley, managing director, said: "Being captain of Newcastle United carries important responsibilities on and off the pitch and this is recognition of Jamaal’s on-going contribution to the role.
"He has become a key member of the squad and a leader in the dressing room, and with many years ahead of him in his career, there is still much more to come.
"We are delighted that Jamaal has renewed his commitment to the club.”
