But now that the Rabbitohs flyer has achieved almost everything there is to achieve in rugby league, he's turning his energy to another childhood dream, becoming a writer.
"I always loved playing heaps of different sports as a kid and footy was one of them," Johnston told AAP.
"But it wasn't until the end of high school that I decided to knuckle down and really focus on rugby league."
He credits his success as a professional athlete to his coaches at Sydney's Endeavour Sports High.
But off field, there's more to the man. Johnson is proud of his Papua New Guinea and Saibai Island heritage and the fact he's become a dad.
And he 's now a published author too, with his first book A Footy Tail - inspired by his love of the game and his son - hitting the shelves in October.
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Johnston has always enjoyed creative writing and throughout his formative years it was something he wanted to pursue.
However, his aspirations were pushed aside as his NRL career took off and then put on hold again, until the birth of his child.
After Sonny arrived, he finally decided to put pen to paper.
"It wasn't until my little boy was born that I was reading a bunch of children's books for him and I had the idea of why not use this opportunity to do the writing I always wanted to do and write something for Sonny," Johnston said.
He wanted to pen something easy to begin with and footy seemed a natural fit.
A Footy Tail naturally revolves around a team of Bunnies and features Johnston and fellow Indigenous teammates Cody Walker and Latrell Mitchell, including their totems.
"I wanted to throw in a bit of Indigenous culture and artwork in there as well, the things that I am very passionate about," he said.
"I'm stoked that I have a book now."
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