The 24-year-old halfback will make his international debut against Fiji after England put out feelers earlier this year to find out if he was interested in playing for them.
Walker was born in England in 2002 because his father Ben Walker was playing with Leeds Rhinos at the time, so it was no surprise that England coach Brian McDermott reached out. Thanks but no thanks, was the reply.
"I was obviously honoured to have a chat but I knew where I wanted to play," Walker said.
"I wanted to represent Australia and my family This is where I am from. I know my family would have killed me if I'd played for anyone else. I am absolutely stoked to be wearing these colours."
Walker will play alongside five-eighth Tom Dearden in the halves at Suncorp Stadium on Sunday night, rebooting a family connection that goes back almost 50 years and a playing connection that started at Brisbane when they were both in the Broncos Academy.
"Tom's mum Andrea grew up two doors down from my grandmother's house in Toowoomba and we went to the same school at St Mary's College," Ben Walker told AAP.
"Tom's uncle Don Saunders was a bit older but he was the captain of the Toowoomba Clydesdales side that won the first Queensland Cup in 1996."
Sam Walker believes it was almost fate that he and Dearden should line up together for their country.
"We have almost grown up together. Our families have known each other for a very long time and we came through Broncos pathways together," he said.
"It's great to be able to be in camp with him and enjoy his company first and foremost and now to be able to play alongside him.Â
"He is a great footballer and a great competitor and I can't wait to see what he brings to the team. I'm sure our combination will work really well."
Walker's rise over the past two seasons has been a tribute to his ability to cope with adversity. This year he had a stellar State of Origin series debut for Queensland and won the NRL title with Sydney Roosters after fighting his way back in record equalling time from a syndesmosis injury.
Winning the World Cup would top it all off.
"A couple of years ago I had an ACL and I worked so hard to get back and play NRL," he said.
"I had a clear goal at the start of this year how I wanted the year to go and I've ticked a few of the boxes so far and there is one more I want to tick.
"Breaking the (selection) news to the family and seeing how excited they were, it is a real honour and the pinnacle of rugby league to represent the country I am so proud of. It is so special.
"I am already learning so much from these great players. I can't wait for the next few weeks."
One of those great players in Walker's club is skipper James Tedesco, who will captain the Kangaroos from his familiar fullback position.
"It's awesome to have Teddy in camp as well. He's such a great leader and I can't wait to run out behind him," Walker said.
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