On Sunday, in the only country in the world where rugby league is the national sport, large crowds gathered from all over the country to watch Olam in the grand final where the Melbourne Storm took on the Penrith Panthers and won in an unforgettable game.

The game had been described as the "Penrith Panthers versus PNG" because of the support Olam had received from his family and fans back home.

"Justin is a testament to what a rural PNG youth can achieve through dreaming big, chasing the dream with hard work, dedication and discipline. Success does not have [to] happen overnight," Papua New Guinea's Prime Minister James Marape said in a statement.

Crammed together around television screens to watch Olam make his grand final debut, his fans in Port Moresby let out loud cheers with every breakaway and tackle. They couldn't have been more proud of how far Olam had come.

"As the second Papua New Guinean to make it on the big stage [for the Melbourne Storm], it was a truly big blessing for every Papua New Guinean," fan Martin Harry said.

"Watching him, knowing that a Papua New Guinean played in the NRL, and now won a premiership, I'm so happy, I'm so proud. This is an achievement for every Papua New Guinean," another fan, Trisha Bai, said.

In his family's home, Gon village near Kundiawa, his parents Mark and Evelyn Olam said they were extremely proud of their son and grateful for the opportunities he had been given.

The village held a feast to celebrate the Melbourne Storm making it into the grand final.

Olam, who comes from a family of strong religious beliefs, prayed with his parents over the phone on grand final day.

They have not seen each other since they visited Australia a year ago.

"I am so happy that he has helped give PNG a good name and rugby league," Evelyn Olam said.

"Young girls and boys around the area were wearing Storm jerseys, T-shirts, caps. The whole country, the province, were backing the Storm. People were painting their faces," Mark Olam said.

Fans in Port Moresby watch Justin Olam make his grand final debut (ABC News - Belinda Kora)

Olam knew from a young age he was going to be a rugby player, his mum said.

She used to find him filling 500ml coke bottles with sand and passing it around with his two brothers like it was a rugby ball.

Olam is the second Papua New Guinean player to play in the NRL without having played in the Australian junior rugby league, after Marcus Bai did so in the 1990s, also with the Melbourne Storm.

NRL Pacific coordinator Mark Mom said Olam's performance was "solid and inspirational".

"He's grown into an exceptional footballer and we're just really pleased in his performance and happy for him that he can celebrate a milestone both personally and for the team," he said.

"I hope he wins more grand finals. He keeps working hard because and I hope that he continues to inspire more Papua New Guinean girls and boys to take up the sport but also achieve their dreams."

It was Olam's hard tackles and dedication to the game that first caught the eye of coach Michael Marum, who selected Olam for the PNG Hunters side in 2016, which was playing in the Queensland Cup.

"We brought him into camp straight away, with his attitude to training, his willingness to work really hard at training, he was aggressive, he wasn't scared of the big boys at the time," he said.

"He wasn't scared at all of anyone and he always put his body on the line every time we had training," Marum said.

Marum said it was not just what Olam had achieved on the rugby field that made him a role model to his legion of PNG fans.

"Justin is a role model because he balances everything right and he's got the respect … when he puts on the jersey, he's proud of where he comes from, and that's one thing that gets everyone behind him," he said.