The 17-year-old midfielder, who has played 28 times for the USA Under 17s and scored eight goals and captained the side in this summer's youth-level FIFA World Cup in Mexico, has joined from De Anza Force in California.
Bright spark: Liverpool expect big things from exciting USA youngster Marc Pelosi (R)
'We're determined to identify the best possible talent globally and I'm delighted we've been able to bring Marc in to the club,' academy director Frank McParland told the club's official website.
Earlier this year, Pelosi had revealed he was contemplating continuing his education in the US by studying at college but admitted the lure of Liverpool was a difficult one to resist.
'College could still be a good option, but it depends on the offers that are coming in,' he said in the summer.
New signing: Liverpool boss Kenny Dalglish has recruited promising American teenage midfielder Marc Pelosi
'Going pro is my first priority. We heard there was some strong interest from Liverpool, and Germany a few [other] places, so I'm just deciding where to go.'
He eventually opted to join the Reds, where he will push to impress first-team manager Kenny Dalglish.
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