The 25-year-old striker put pen to paper on a five-year deal at St Jame's Park to become Benitez's second signing as Newcastle boss.
Gayle has worked his way up from non-league football after spells with Dagenham & Redbridge and Stanstead, before ventually landing in the Premier League with Crystal Palace.
And Benitez believes the forward has the attributes to take United back to the top flight after their relegation last season.
He said: "Dwight is a great player, a proven goalscorer, and it is fantastic news that he has joined us.
"He has a big personality, a lot of energy and pace. He is a good finisher also, so he will add goals to our squad, for sure.
"He knows English football well, too, and that is important in the Championship.
"I am sure Dwight will want to prove he can make a big difference to our team and I am looking forward to working with him."
Benitez had earlier warned that new players must be able to handle the expectation at Newcastle. Read his comments here.