Longstaff has signed a new four-year contract at the club after impressing in the summer on his return from a loan at Blackpool.
Rafa Benitez promoted Longstaff to his first-team squad after the midfielder caught the eye in pre-season.
Longstaff is grateful for the opportunity he was given by Benitez, who has spoken highly of his “quality and talent”.
Asked about Benitez’s influence on him, Longstaff said: “He’s been massive.
“He’s different in terms of what he wants from you. Out on loan, it’s about running around and tackling people, but he’s so smart in the way he does everything.
“He wants you to think the game and see the game differently. For me, being a young lad, he’s been great with me.
“He speaks to me and explains every little detail, so it’s as simple as it can be. I’ve loved working with him so far, and hopefully it continues.
“It’s unbelievable the feeling that you get when they give you a contract. They’ve got faith in me, and I really appreciate that.
“It’s about me showing the same trust they had in me and going out and improving and hopefully repaying them with performances.”
Longstaff spent last season on loan at Blackpool. The 21-year-old scored nine goals from 45 appearances for the League One club.
Longstaff – who will play in tomorrow night’s Checkatrade Trophy tie against Macclesfield Town at St James’s Park if he’s not needed for the midweek Premier League game against Everton at Goodison Park – had had a spell at Scottish Premiership club Kilmarnock the previous season.
And the North Shields-born player believes those loans prepared him for the rigours of first-team football at Newcastle.
“I can honestly say that if I hadn’t gone out on loan, there’d be no chance of me being in the first team now,” said Longstaff, who made his senior competitive debut in the club’s Carabao Cup tie against Nottingham Forest in August.
“I think it’s what you have to do. You have to prove to the staff here and prove to the lads that you can be trusted in those situations.
“That’s the only way you’re going to learn – by doing it on a Saturday-Tuesday in some not very nice places or grounds.
“That’s the only way for us young lads to get up here (to first-team squad), unless you’re unbelievably talented, like Rolando (Aarons), who came straight through.
“I think everybody’s got to go out on loan and put in those hard yards to come back up here and get a chance.
“I’ve done that now. It’s at least allowed me to spend six months with the first team and learn a different side to the game and a different style. Every young lad should be looking to do that.”
Longstaff is now focused on taking the next steps at his boyhood club.
“I can’t wait to carry on the hard work and keep learning and improving and try to get into the team in the future,” said Longstaff.
The club opened contract talks with Longstaff in the summer.
Longstaff said: “We’d been talking since the summer.
“When I ended up staying, it gave a bit more time to get it sorted.
“I’m just delighted it’s all done. I just focused on my football.
“That’s what the manager said to me. I can now 100% focus on football – no distractions.”