Justin Olam was born and raised in Gon, a small village in the Sinesine Yonggomugl District of the mountainous Chimbu Province, Papua New Guinea.

Olam was educated at Rosary (Kondiu) Secondary School in Chimbu and attended the Papua New Guinea University of Technology in Lae Morobe Province where he graduated with a Bachelor's Degree in Applied Physics.

Whilst studying for his degree, Olam began playing rugby league for the Unitech Spartans in the PNG Universities competition.

[3] In 2017, he played in every game for the Melbourne Storm feeder club Sunshine Coast Falcons in the Intrust Super Cup competition through to the grand final loss against his former team PNG Hunters who came from behind to score in the dying minutes and won 12–10 at Suncorp Stadium.

His contract was extended for another two years after impressive string of performance in the reserve grade which will keep him at the Melbourne Storm till the end of the 2020 NRL season.

On 23 October, he was again named in the Papua New Guinea Kumuls squad for the 2019 Oceania Cup (rugby league) Pool B Ox & Palm Pacific Invitational Test against Fiji Bati at Christchurch Stadium in New Zealand on 9 November 2019, and Great Britain Lions on 16 November 2019 at the National Football Stadium in Port Moresby Papua New Guinea.

In round 16 he scored his second career hat-trick against Manly-Warringah.On October 16, in Melbourne's Preliminary Final game against the Canberra Raiders at Suncorp Stadium, Olam scored a try in the 23rd minute off a kick from teammate Ryan Papenhuyzen, miraculously leaping over both Papenhuyzen and Canberra player Hudson Young while avoiding the arm of Nick Cotric to catch the ball mid-air before grounding it.

On the 25 October, Melbourne went on to win the Grand final, beating the Penrith Panthers 26–20 in which Olam scored a penalty try in the fourth minute of the match.

[6] Olam played a total of 25 games for Melbourne in the 2021 NRL season as the club won 19 matches in a row and claimed the Minor Premiership.

Afterwards, Melbourne star Cameron Munster took to Instagram to vent his frustration at teammate Olam being snubbed for consideration in the Dally M team of the year.

[8] In late 2022, Olam represented Papua New Guinea at the 2021 Rugby League World Cup playing all four games before they were eliminated by England at the quarter-final stage.

[9] On 14 February, it was announced that Olam would miss the opening six rounds of the 2023 NRL season due to an arm injury he sustained during the clubs pre-season trial against the Sydney Roosters.