Back in the Maze, Newt was pretty much the second-in-command to Alby. But when Alby died, Newt became the leader. But then, all of the kids were given tattoos overnight in the dormitories, and Minho's said "The Leader"—so that's apparently it for Newt's role as leader.
Now Newt is known as "The Glue." You can guess what this means: Newt is the guy who holds all of the Gladers together. He's the more logical version of Minho: while Minho would run into a group of angry Cranks without any weapons, Newt would probably stay back and ponder the situation. He'd be like, Hmm, maybe we shouldn't attack the Cranks without any weapons. Good thinkin', Newt.
When Minho becomes the leader, it's pretty clear that Newt gets a bit rattled, especially given the fact that Minho can pretty often be ridiculous. When Minho predicts that there might be psycho girl ninjas somewhere, for example, we get this from Newt: "'Psycho girl ninjas?' Newt repeated, his voice showing he was surprised, if not annoyed, by Minho's attitude" (20.13).
Newt wants to be the leader, but he understands his new gluey role—and part of being "The Glue" is stepping back letting Minho lead.
Another part of being "The Glue" is having a firm grasp on the Gladers as a unit. Thomas, for example, doesn't really know everyone's name (which is pretty bad, considering there are only about twenty Gladerss left when they enter the Scorch), Newt keeps tabs on every one of them:
"And that's all you can buggin' think about? What about the people who died, Minho? Jack's missing. So is Winston—he never had a chance. And"—he looked around— "I don't see Stan or Tim, either. What about them?" (25.42)
Pshh, Stan and Tim? These names haven't even been mentioned until Newt recognizes that these guys are missing. And while Newt keeps tabs on his Group, he's also good at looking at their situation from a rational standpoint:
"If someone had wanted to kill us, why wouldn't they have just killed us? Why would they send us to a huge place with a house and a barn and animals? And because we had no other choice, we accepted it and started working and exploring." (9.13)
It's Newt who comes to the conclusion that the Maze wasn't just a random test to kill a bunch of kids. This piece of Newt-wisdom, in fact, is what restores a lot of Thomas's confidence. Remember, WICKED is controlling Variables—and Newt makes sure the Gladers know this so that they don't all give up.
Overall, Newt's kind of a sub-leader, or a leader acting more behind the scenes that out in the open.
Plus, we'd just like to note that this dude's U.K. accent is a-ma-zing: "You think I have a bloody clue? Bunch of crazies want to eat us for breakfast, by the looks of it... All this noise is driving nails through my buggin' skull" (3.9).
Seriously, this bloke says "bloody" and "buggin'" as often as a Bostonian says "wicked."
No, not that WICKED.