The 22-year-old joined Quins from Saracens last season and made 10 appearances in all competitions in his first year at the club.
"The whole experience has been great from day one and I can't wait to carry on wearing the shirt in the hope to bring more success," he said.
Morris, who can also play on the wing, was part of the England Under-20 side which won the 2014 Junior World Cup.
Harlequins full-back Aaron Morris has signed a new contract.