The 20-year-old joins for a reported £30m plus £5.5m in add-ons after a breakthrough campaign in Ligue 1, and has signed a contract at St James' Park running until the summer of 2031.
Bamba made 18 Ligue 1 appearances last season, ten of them starts, registering two assists, and also featured for Monaco in the Champions League, including both legs of their knockout tie against Paris Saint-Germain, as the French club reached the competition's later stages.
His performances earned him a nomination for the 2026 European Golden Boy award, underlining the rapid rise that has taken him from fringe squad player to full international prospect within a single season.
Newcastle United manager Eddie Howe said he was delighted to add the young Frenchman to his squad.
"I'm really pleased to see Aladji become a Newcastle player. He's another exciting, young signing who we're really looking forward to working with," Howe said.
Howe went on to outline the qualities Bamba will bring to his midfield options.
"He operates in a deeper role but has the ability to contribute all over the pitch, which he demonstrated in both Ligue 1 and the Champions League last season," the Englishman added.
Bamba was also given the chance to speak following the announcement of his arrival.
"I'm very happy to be here – it's a new challenge and I can't wait to get started. I was very excited when I heard Newcastle were interested in signing me," said the Frenchman.
"I know about the history of the club and I've visited the stadium already, which is amazing. I can't wait to be on the pitch there and hope to have some great times with the fans."
Bamba's arrival comes as Newcastle continue to reshape their midfield following Sandro Tonali's departure to Tottenham this summer, with the club having moved quickly to secure one of France's most promising young talents amid interest from elsewhere in Europe.
Howe has already made a number of additions to his squad this summer as Newcastle look to build on last season's Premier League campaign, with further midfield reinforcements not ruled out before the transfer window closes at the start of September.