Irish-born Mullen made his international debut for the United States earlier this year, starting in victories over Canada, Scotland and Russia, and has been playing his club rugby for Major League side Houston SaberCats.
"Paul has broken through to the full international scene in quite a big way over the past few months, and been part of a rapidly-improving American Eagles side," Dean Richards, Falcons director of rugby, said in a statement.
"His presence will further bolster our front-row resources going into the new Gallagher Premiership season as we look to improve yet again on what was our best league finish for 20 years."
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Falcons begin their Premiership season against Saracens on Sep. 2.
(Reporting by Hardik Vyas in Bengaluru; Editing by Matthew Mpoke Bigg)
