This "extraordinary, ordinary man", as a judge called him, is today being honoured with a George Medal, the UK's second-highest civilian award for bravery.
He spotted Mohammad Farooq looking upset and agitated outside St James's Hospital in Leeds on 20 January 2023.
He was there to commit mass murder at the entrance to the maternity wing, killing nurses and potentially patients too.
"[He] seemed like he might want a chat or had some bad news, so I went over and asked how it were. And it just went from there really," says Mr Newby.
Farooq, a trainee nurse at the hospital, had a pressure cooker packed with 10kg of gunpowder in a bag and hoped to kill nurses by luring them outside with a bomb threat.
Mr Newby, 35, began chatting to him as he was "fiddling about, swaying back and forth" and initially thought he might be upset about a sick relative.
"He looked out of place; I just went over to see if he was alright. Have a chat, see if I could cheer him up and make him feel better," he says.
Mr Newby - who was receiving treatment at the hospital and still had an IV line in his arm - also noticed a suspicious bag about 6ft away.
Farooq, 28, was far from an anxious family member.
His trial later heard he was a lone-wolf terrorist, inspired by Islamic State, and had chosen his target due to a grievance with nurses on his ward.
"He was watching every nurse come out when they were going for their fags. He was watching this bag all the time," Mr Newby says.
Growing concerned over why the bag was standing alone, he asked Farooq plainly what was inside.
"He ummed and ahhed at first, then told me what were in it - told me there were a bomb in it," he says.
His scepticism disappeared in a heartbeat when Farooq opened the bag and showed him the device - a DIY bomb he'd rigged up while sitting in his car outside the city's Roundhay Park.
"That's when I knew this is real. It were like a pressure cooker - like a slow cooker with wires out the top," Mr Newby says.
'Befriending' the bomber
Worried that shouting or running would panic Farooq into detonating the device, the 35-year-old stayed calm despite the risk to his own life.
"I stuck with him, trying to take his mind off what he wanted to do, get to know him, see if I could change it," he says matter-of-factly.
"You don't have time to think how you're feeling, you just think of people around you."
Farooq had earlier sent a bomb threat by text to an off-duty nurse in the hope of getting people out to the car park - but they didn't see it for nearly an hour.
He had changed his plan and was now waiting for a shift change to go inside and explode the bomb.
As the suicide attacker opened up about the likely radius of the bomb, Mr Newby was figuring out how to coax him further from the building.
"I worked out in my head if I get him to the middle - if he does decide to set it off - it'll just set the doors off.
"It won't take the building out. Less damage and less people."
Playing for time, he tried to form a bond with Farooq by "talking about my issues, his issues, why he were doing it".
"He told me he wanted to get them back for what they've done. I said 'there's ways of doing it mate - this is the wrong way'," recalls Mr Newby.
"Then I twisted it, made him feel better than me... so I looked like the one who had more problems."
But the bomb was still just feet away, and a sudden change in Farooq's mood could have been catastrophic.
Mr Newby knew he had to somehow raise the alarm, but his options were very limited as the grounds were nearly deserted.
"It was just me and him, there were no one there I could send a signal to or anything."
However, he managed to get Farooq to leave the bag near a bench while he spoke to him a few seats further along.
With the terrorist's back to the hospital, he seized his chance when a security guard appeared for a smoke about 10ft away. But agonisingly the man didn't see his gestures for help.
"I were trying to flag him down but he didn't look over. Then he walked away - and it were like back to me and him now," Mr Newby says.
'Can I have a hug?'
Returning to his strategy of trying to occupy the bomber, he was mentally preparing to be there until morning when the hospital got busier. In the end, the stand-off lasted about six hours.
However, the situation took an unexpected turn.
"He asked me to stand up and give him a hug, so I said 'yeah, have a hug mate'. And then he said, 'right, I want you to phone the police before I change my mind'."
Farooq volunteered his own phone as Mr Newby's was out of battery.
But as he entered the pin, it flashed across his mind that he could be playing into his hands and the number might detonate the bomb.
Farooq reassured him - but there was another threat.
When the 999 controller asked him to check if he had weapons on him, Farooq pulled out a gun (later revealed to be an imitation).
"He unzipped his coat and pulled a gun out to me for about three or four seconds," he says.
"[I] grabbed it and twisted it round, pointing the handle towards me. I said, 'look, I don't want to touch that, can you put it down on the bench'."
Armed police soon descended on the hospital, bundling Mr Newby into a van for his own safety and ending his six-hour stand-off with Farooq.
He was found guilty, sentenced last year to a minimum of 37 years, with Sheffield Crown Court hearing how he immersed himself in "extremist Islamic ideology" and wanted to kill as many nurses as possible.
Farooq first planned to attack RAF Menwith Hill in North Yorkshire but switched targets after finding it was too well guarded.
Investigations also revealed a poison pen campaign against colleagues after he had to repeat a year of his course because he was always sick and didn't pass exams.
Nathan Newby's humanity and bravery that night almost certainly saved lives.
He says the danger and potential repercussions didn't hit home until he was back in his hospital bed.
"If I hadn't got that chest infection, got rushed in, and had been at home, he'd have gone for it and I'd be seeing it on the news."
