As we sit across a coffee shop table reflecting on his stella boxing career and discussing his decision to retire, his whole demeanour reflects that fact.
It would be wrong to suggest there were not a few pangs of what might have been, or mentions of things that may have been done differently.
But McDonnell is certainly comfortable with his decision to hang up his gloves and proud of the legacy he will leave in the ring.
And so he should be.
It was one of the most unlikely success stories in sport. Often told, well worth repeating.
A journey which took in a cabinet full of titles and two attempts to become world champion began with a drunken boast of ‘if he can do it, so can I.’
The ‘he’ in that instance was twin brother Jamie who hours earlier had become European bantamweight champion in the south of France.
A suggestion that McDonnell could follow in his brother’s footsteps was laughed off by those present, who knew full well that he loved a pint or two.
At that stage, in March 2010, the concept of him stepping through the ropes for a professional fight seemed exceptionally unlikely.
What he would ultimately go on to achieve was frankly impossible.
Eyebrows were raised when he walked through the doors of the gym then run by Stefy Bull and Dave Hulley in Mexborough, a week or so after his claims of matching his brother’s achievements that had been dismissed as booze-fuelled rather than genuine.
His appearance was dismissed at first as a flight of fancy but McDonnell kept coming back, kept working hard and kept demanding more from the coaches.
It was an early indication of the dedication and work ethic that McDonnell would demonstrate throughout his career that would ultimately lead to the success that came his way.
Such determination made him incredibly easy to get behind.
He carried the weight of being Jamie McDonnell’s brother around with him for a long time, particularly after his twin won a pair of world titles.
There were inevitable comparisons in his early fights. He had the same rangey frame of his brother, moved in similar ways and even made the same exclamation noise every time he threw a punch.
But the comparisons were an annoyance he was determined to extinguish. Arguably it fired him on just as much as his own natural work rate.
A draw in his fifth fight against Ashley Lane suggested the ceiling of success may not be a particularly high one but within two fights he was Central Area champion after stopping Scott Gladwin - sparking an incredible run.
Beating the tricky Paul Economides suggested the ceiling was being raised, but be blitzed through it with a pair of classy demolition jobs against rated pair Ross Burkinshaw and Josh Wale to move himself into British title contention.
Even when he stopped Leigh Wood to claim the British crown in February 2014, there were suggestions that would be the pinnacle of his career. And that would have been no mean feat given many fighters dream of taking the Lonsdale belt, while Wood has progressed and is now a world champion.
A barnstorming rematch with Wale on a raucous midweek night in Leeds was probably the best fight McDonnell was involved in as he held onto his British crown via a split decision draw.
In successfully defending the title he had earned the right to progress to international level - and again, he quickly showed himself to be worthy of the status.
He outpointed the tough, fearsome Vusi Malinga in Hull to win the WBO Intercontinental title, which offered the first real suggestion he could content for world honours.
Interviews at the time would often centre on whether he could quite believe how far he had come in such a short space of time. He was more often than not bemused by the suggestion, which led to this writer ceasing to ask as he continued to hit milestone after milestone.
The European title was won and defended in back-to-back outings in Sheffield against Oleksandr Yegorov and Jeremy Parodi.
Five years after his brother won the European crown, McDonnell had succeeded in proving ‘if he can do it, so can I.’
But he would not stop there.
By February 2017 he was in the ring with a world title on the line. His opponent in Hull was 28-0 Mexican Rey Vargas, a formidable opponent.
While Vargas always had the edge on the night, McDonnell never went away and gave as good as he got in the later rounds to send the fight to the cards where the Mexican earned only a majority decision rather than a unanimous one. Vargas has still never lost in his career.
McDonnell emerged with tremendous credit, enough for him to remain in contention for world honours.
And he would earn the rare opportunity to contest a world title in America when he fought Daniel Roman for the WBA crown in October 2018.
That came after career best performances in seeing off hot prospect Gamal Yafai in devastatingly dominant fashion before controlling his clash with veteran Stuart Hall in Newcastle.
Roman proved too good on the night in Chicago and stopped McDonnell. He too has gone on to have a stella career.
McDonnell looked to rebuild again and was happy to step back to small hall shows to do so before his opportunity at European level at featherweight came last year - ending in frustrating fashion with a bad cut seeing the fight waved off.
The pandemic may have enforced more intense thought over retirement but McDonnell simply took it as a sign that he had done enough.
Had he taken the European featherweight title from Andoni Gago on that night in Barcelona in April last year, he may well have retired anyway.
He continues to work as a plasterer but is in a position where he can dictate his workload rather than being forced.
He prioritised more time with his wife Sophie - the rock that backed him all the way and kept him grounded - and their two sons.
And, most importantly, he is not tempted by a return, even after calls offering fights against high profile opposition he would have jumped at the chance of facing in the past.
So many professional sports people end their careers with regrets, frustration and ill-health.
The fact McDonnell has walked away from the ring happy, healthy and proud may be his greatest success of all.