However, the main reason the hulking Yorkshireman is so delighted to play is that, after their current tour of New Zealand and Tonga, he genuinely does not know if the opportunity will arise for him – or anyone else – any time soon.
It has been 12 years since the Lions last played so the enormity of the occasion as they face Tonga in Hamilton is certainly not lost on anyone.
Indeed, a whole generation of international rugby league players have only ever known England and the home nations.
Dewsbury-born Walmsley, 29, has enjoyed a dream season after helping St Helens finish top by a record 16 points, reach Wembley and win his second Grand Final.
“It’s been a wonderful season,” he said.
“But to be part of a Lions tour and being around so many exciting, talented players in such a good squad, I find myself pinching myself.
“I’m really looking forward to putting the jersey on and being made a Lion.
“It’s obviously such a prestigious honour which has not happened for a long time now – and who knows when it will happen again?
“So, to be given this opportunity I’m very grateful and hopefully I can make the most of it.”
The former Batley Bulldogs front-row has faced Tonga in New Zealand before having come off the bench during England’s epic 20-18 2017 World Cup semi-final win at Auckland.
But Walmsley then missed last year’s home series with the Kiwis having sat out most of the season following neck surgery.
He has quickly settled back into Wayne Bennett’s squad, which is largely English players, and said: “Wayne’s been building this squad for a few years now – since 2016.
“And he’s very big on not just being a good player but you have to be right for this squad off the field as well as on.
“He’s very big on being a good person and doing what’s right with people and we have created such a good camp here over the last few years.
“It does make it feel like a club from home.
“Obviously we’re all playing for different teams in the league,” he said.
“But when you come here either as an England international or Lion now, you are very much part of a new team.
“We’re all looking forward to getting going against Tonga and facing what will be a tough challenge.”
He added: “Missing out on the internationals last year was tough.
“But at the same time I was so happy to see the boys do as well as they did – beating the Kiwis three times out of four – is such a great achievement.
“I was happy for people like Luke Thompson and Tommy Makinson, too, to really come to the stage and put in such good performances.”