Laybutt is the fifth Kumuls representative to sign with the PNG Chiefs, following Alex Johnston, announced as Player #002.
The club's other named signings include development players Finley Glare, Gairo Voro and Morea Morea.
The Chiefs have named Laybutt, 24, as their eighth player ahead of joining the NRL in 2028.
He has agreed to a two-year deal and will move to Port Moresby at the end of 2027, leaving the North Queensland Cowboys, where he made his NRL debut in 2023.
Laybutt played all three matches for PNG at the 2026 Rugby League World Cup and can cover wing, centre and fullback.
He played fullback in the Kumuls' 34-12 loss to England last month.
"We are delighted to have signed Zac, and his signing is particularly meaningful for us as we build a club that proudly represents PNG," PNG Chiefs chief executive Lorna McPherson said on Tuesday.
McPherson said Papua New Guinean players could strengthen the club's identity and inspire young local talent by demonstrating what was possible in the NRL.
"Zac is a quality young man who brings a willingness to work hard for the team, and he will join the club with good NRL experience and a bright future ahead of him," head coach Willie Peters said.
Peters said the Chiefs expected Laybutt to keep improving and looked forward to his development with the team.
The club is expected to announce more signings in the coming days, including Canberra Raiders second rower Hudson Young.