West Brom will also welcome a proven Championship goalscorer into their ranks in the shape of Gayle.
Rondon, who has scored 28 goals in 120 appearance for the Baggies over the past three years, posted a goodbye message to fans on social media. "They made me feel at home from day one and I'll be eternally grateful for how they supported my family and I. I wish you all the best".
Rondon will provide Newcastle with the physicality that Gayle lacked and act as a focal point in attack.
Albion were not willing to part ways with him on loan unless they received Gayle in response.
Rondon is the archetype of a Premier League striker.More news: Bill Belichick, Robert Kraft surprise Randy Moss at his Hall induction
"As the first Japanese Newcastle United player, I am honoured to be a player for such a big club".
But Benitez clearly feels more must be done, adding: "I am not happy we are looking to just survive every year".
Venezuelan global Rondon may not be the most prolific striker, hitting just 24 goals in 108 Premier League games for the Baggies, but he has the physicality and work rate Benitez is looking for.
There were 450 minutes of football in the five friendlies and only six players have featured for half or more of the total possible time.