The legal age for buying tobacco products and e-cigarettes on Guam will rise from 18 to 21 next year.
This comes after the governor, Eddie Calvo, allowed a bill passed by lawmakers earlier this month to lapse into law.
The Pacific Dailys News reports that Mr Calvo veoted a similar bill last year, saying it was the wilful intrusion into lives and personal choices.
But this time, a majority of senators voted in favour of the change, making it veto-proof.
Guam's smoking rates are the highest in the United States, and the law change has been welcomed by health workers and the American Cancer Society.
The age restriction will take effect from the 1st of January 2018.