The Leicester City striker arrived on Tyneside earlier today ahead of the 11pm transfer deadline.
And United have completed a deal for the 29-year-old.
Slimani underwent a medical this afternoon after travelling to Newcastle on a private jet.
“It’s a great thing for me and for Newcastle," said Slimani. "I’m happy to be here. Hopefully, I can come here and be able to give them a hand.
“Knowing the power of the fans and crowd here and how great they are, and also speaking to the manager, it gave me the confidence that this was the right choice.”
United manager Rafa Benitez said: “Slimani is a player with experience in the Premier league, and obviously we were looking for that.
“He is a player who can fight with defenders, challenge and score goals. Hopefully, he can give us some experience and some different characteristics to the strikers that we have at the moment.”