Dwight Gayle has moved in the opposite direction to spend the season on loan at the Hawthorns.
Speaking about the move, Rondon said: "It's an honour to be here and I'm excited to get started with my team-mates.
"The clubs were talking for a long time and now I'm focused on the season to help my team-mates to get the points to do well this season.
"It's one of the biggest clubs in the Premier League and I knew about the interest of the gaffer, so I'm happy to be here."
So excited to have joined @NUFC!! Can't wait to play in this historic shirt! pic.twitter.com/oAIxDekmdA
— Salomón Rondón (@salorondon23) August 6, 2018