The 24-year-old France international, who has been repeatedly linked with a move to the Magpies this summer, has been tied down to the Premier League club until 2020.
Speaking to his new side's official website following the confirmation of the transfer, Cabella said: "It is great to finally be a Newcastle player. This is a move that I really wanted to make as I have heard nothing but good things about Newcastle United from everyone I spoke to.
"I wanted to join a great English club and that is why I have arrived here. I'm looking forward to pulling on the shirt and playing in this magnificent stadium, and I will give this club my maximum."