Next Saturday night he will be in Hull to face unbeaten Mexican banger Rey Vargas, with the vacant WBC super bantamweight title up for grabs. Boxing’s prestigious, much sought after green belt.
It will be his 19th fight, a startling fact given he had no amateur experience other than five bouts as a junior.
Life has been a whirlwind since his debut a little more than six years ago. Rapid improvement saw Central Area, British, WBO intercontinental, European and WBC Silver titles claimed.
And before he knew it, he found himself where he is today - a world title contender mere days away from a life-defining night.
Meeting him at his home in Hatfield, McDonnell is a bundle of energy, powered by both excitement and nerves.
Keen to relax after a hard session in the gym and ahead of a long run with world champion twin brother Jamie, he lounges on his sofa.
But it is hard to imagine he will ever truly relax before next Saturday night is over. He shuffles around a lot, repeats the same points again and again.
Even though he admits it is hard to take his situation in, he is fully aware of what awaits and what could await in the future.
So while relaxing may be difficult, there is an incredible amount of focus on the task at hand.
“I’m waking up in the morning excited for fight night,” he said.
“It can be a bit daunting going into a fight because you’ll be thinking that you’re not fit enough or you’ve not done this and that.
“But I’m waking up wanting it. I’ve got that buzz.
“I know I’m at fight fitness and I’m looking forward to it.
“We’ve had a really good camp. We’ve nailed it over the last two weeks and we’re getting ready for showtime.
“You get that little bit more of a buzz about it, a bit more seriousness.
“It’s not that I’m not always switched on. You can just tell that you’re that bit more focused.
“Little things in the past that you might be looking forward to or you’re desperate for like a nice meal, nothing like that bothers you.
“You just want to do everything possible.”
Victory will not only deliver a world title and see him emulate the success of his brother, it will open up life changing prize pots that could secure his future and only have to pick up his trusty plasterer’s tools on his own terms.
On his TV, a couple is looking around a property abroad, considering whether to buy. And he cannot help but be distracted by it.
“My favourite thing to watch are these homes in the sun programmes,” he said. “I record them.
“I want to be doing that, buying a place abroad.
“I want to be mortgage free and have a holiday home.
“Then I wouldn’t mind going back to work, with that pressure off.”
McDonnell’s rise has been an incredible storybook tale.
Seven years ago, in a drunken state in the south of France as he celebrated brother Jamie winning the European title in Cannes, he stood up and declared to the party ‘If our kid can do it, so can I!”
Gathered friends and family laughed, dismissing it as a typical drunken boast.
A year on, he was a professional boxer, showing slight similarities to his brother which suggested a semi-decent domestic career could be on the cards.
And now, with a trophy cabinet many fighters would give their right arm for, he sits of the verge of the ultimate honour.
In the past, the 30-year-old has found it difficult to reflect on how far he has come in such a short space of time.
While that remains the case to an extent, a world title opportunity has put him in much more of a mood to assess his achievements.
“You’re just on that journey at the minute,” he said. “But every now and again you think ‘Wow, look where we are now.’
“You couldn’t really write this.
“From the pressure of living up to our kid, I’m on the verge of beating him to a better title.
“And I’ve not been given anything. I’ve worked hard.
“There’s more pressure on me because I’ve always been compared to him.
“But now the comparisons are good comparisons.
“I’ve been in the deep end. It’s 18 fights. There’s been no big hype about me.
“If I can win a world title in less than 20 fights, the WBC title, who out there does that?
“No amateur career. A small little team. I’ve plodded along and I’m here.
“Vargas is going to have to pull it out of the bag to beat me.
“I know I’ve got to do the same but I’ve got it in me.
“I want it so bad. Let’s just see how it goes.
“I’m 100 per cent going to win it, no doubt about it.”
Sitting days out from the night of his life, the dream is not so unimaginable any more.