The second row has been in outstanding form, especially in the opening 38-17 hammering of France, and fully earned being rested for the 36-0 defeat of Italy a fortnight ago.
His evolution into becoming a stalwart of Andy Farrell's Ireland side stemmed from making a bold move in 2016 to Welsh region Scarlets, after failing to break through at Leinster.
Not only did he help Scarlets win the 2017 Pro 12 title - ironically beating his present province Munster - but such was his form that his then director of rugby Wayne Pivac tried to get him to stay on.
This was with a view to Beirne becoming qualified for Wales, due to the residency rule at the time.
Pivac was subsequently to take over at the helm of the Wales national team before being fired and Warren Gatland returned.
"I only ever wanted to play for Ireland, that was the reality," said Beirne last year.
"And when it became a talking point that there was an opportunity to play for Ireland, the only thing I wanted to do was come back and play for Ireland.
"So I didn't have a conversation with Warren (Gatland) but I did have a conversation with Wayne before I left Scarlets and he tried to encourage me to stay because he did say the World Cup was the following year (2019) and I'd be qualified for it and all that.
"But I think I'd made my decision before that, I wanted to wear green for the World Cup not to be in red."
'Real standard bearer'
Beirne has had little reason to regret his call, although sparingly used by Joe Schmidt in the national team, he has become a regular since Farrell took over after the 2019 Rugby World Cup.
Easily to spot on the pitch due to his blue scrum cap Beirne produced a huge performance in the opening victory over France in Marseille.
His reassuring presence alongside the inexperienced Joe McCarthy helping his team-mate's man of the match display.
"Tadhg is an incredible player," said his Munster teammate and Irish great Conor Murray.
"He spent a lot of time in Wales playing, probably did the hard road to get to where he is now and he's fully deserving of the plaudits he's getting."
Beirne is renowned for being a good team-mate to have around when it is downtime - he took to baking biscuits on the British and Irish Lions tour of South Africa in 2021.
"I know Tadhg really well," said Murray.
"An incredibly laid back, relaxed fellah right up until to kick-off, and then as soon as he puts the blue scrum cap on he turns into something else.
"His form has been incredible over the last few years and he's a huge asset to us."
For Ireland's defence coach, and another former Scarlets back-rower Simon Easterby, Beirne is always thinking on his feet.
"He had time away from Ireland for a couple of years in Wales and I think he was able to grow as a person but also as a player," said Easterby.
"He's such a good rugby brain. He's got real smarts about him.
"He's tough and just the sort of player in your team that is looked upon as a real source of inspiration and a real standard bearer in terms of performances."
And what about his Harriet's loyalties come Saturday?
"My wife might be Welsh, but she'll be wearing green," he said.
