Lomax's Chiefs deal comes nearly five months after a highly-publicised legal battle ended with his former club Parramatta blocking a mooted move to Melbourne.
The Eels had released Lomax so he could join subsequently-axed rugby union competition R360, and retained his player rights through 2027.
Lomax, 26, has spent this year with Super Rugby Pacific's Western Force.
The former NSW State of Origin representative is currently injured but will remain with the Force before joining the Chiefs for their inaugural pre-season late in 2027.
PNG confirmed Lomax's arrival on Sunday, unveiling him to fans in Port Moresby.
"PNG, thank you very much guys. I just want to say, thank you so much everyone. It's an absolute privilege," Lomax said.
"I am super honoured to be committed to you guys and it's such a great opportunity for all of us boys and everyone that is going to be coming over to the PNG Chiefs.
"We are going to shock the NRL, I am telling you, and I can't wait to be apart of it."
Lomax joins Jarome Luai, Alex Johnston and Connor Watson on a star-studded roster for 2028, while the Chiefs have also been linked with cross-code star Joey Manu in recent days.
Melbourne five-eighth Cameron Munster has been granted permission to negotiate with the Chiefs and Storm coach Craig Bellamy publicly gave the Queensland captain his blessing to sign on Friday.
Lomax played 133 NRL games across his first stint in league, most of those for St George Illawarra before a move to the Eels in 2025.
He left rugby league at the peak of his powers, considered one of the most well-rounded wingers for his aerial abilities, finishing and athleticism.
Lomax played every game of the 2024 and 2025 State of Origin series, winning the shield in the first of those.
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