Lascelles joined United in the summer of 2014 from Nottingham Forest, where he had come through the youth set-up to start his career.
He returned to the City Ground immediately, spending the entire 2014/15 season on loan at his former club to aid his development.
The centre-back became a regular in the Newcastle side during the second half of last term, particularly following the arrival of manager Rafa Benitez, and has made 21 appearances for the Club to date, scoring two goals.
“It’s an unbelievable feeling for a manager like Rafa Benitez to give me the captain’s armband at a club like this,” said Lascelles.
“It is a lot of responsibility for a young player but I will always give my all because I want what is best for the team and the Club.
“It is such a proud moment for me and the biggest in my career so far.
“It is nice for someone to show that much trust in you, and I want to repay the manager’s faith by leading this team back into the Premier League.”
Newcastle United manager Rafa Benitez added: “We have a few players now in the squad who have the character to be captain, but Jamaal has proven himself to be a leader and a big personality in the dressing room and on the pitch.
“At the end of last season he really developed as a character and a man.
“I am pleased that Jamaal will be our captain, but I have also said to other players that they must too show their character, strength and leadership qualities to support the team.”