Slimani is a player with Premier League experience,” said Newcastle boss Rafael Benitez.
“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 we have at the moment.
“Dubravka is someone with some experience. He will need to settle down quickly as he is a player coming from abroad, but he is very agile and he can play with his feet.
Newcastle have scored only 22 goals in 24 Premier League games and they had been linked with moves for Liverpool forward Daniel Sturridge before he joined West Brom and Feyenoord striker Nicolai Jorgensen.
“It’s a great thing for me and for Newcastle,” Slimani said.
“I’m happy to be here. Hopefully I can come here and be able to give them a hand.”