The Wallabies talent walked away from rugby last year to spend 10 weeks at Florida's IMG Academy completing a crash course in American football.
That culminated in a trial in front of scouts from all 32 NFL teams, the 25-year-old impressing enough to be scooped up by the Chargers on a deal announced on Thursday.
Able to play any backline position in rugby, Petaia is likely to be tried as a tight end by the Chargers, who finished second in their conference and lost in last season's wildcard round to the Houston Texans.
Established in 2017, the IPP program is designed to offer elite athletes from around the world with experience in other sports the opportunity to improve and develop their skills to earn a spot on an NFL roster.
Under new rules introduced before last season, the Chargers can carry Petaia in an extra roster spot and activate him at any stage.
Petaia played 31 Tests for the Wallabies, debuting for the Queensland Reds when he was 18 and becoming the youngest Australian to play at a World Cup the following year.
Injuries routinely set the versatile talent back but at his best he showed explosive athleticism coupled with terrific hand and foot skills.
Training as either a smaller tight-end or bigger wide receiver, Petaia's professionalism had impressed observers, who regarded this crop as the best-performed IPP squad yet.
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