Primarily a defensive midfielder, Aladji enjoyed a breakthrough campaign with Monaco in the 25/26 season, making 25 appearances across all competitions as the club secured a seventh-place finish in Ligue 1, qualifying for the Conference League.
Aladji was named on the 2026 European Golden Boy award nominee list earlier this year. The annual award, previously won by the likes of Lamine Yamal, Kylian Mbappé and Jude Bellingham, recognises the best Under-21 talent in European football.
Aladji, who will wear the number eight shirt for the Magpies, has penned a five-year deal at St. James' Park and is raring to go ahead of "a new challenge" in moving away from France for the first time in his fledgling career.
"I was very excited when I heard Newcastle were interested in signing me," Aladji said.
“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."