The Pilgrims are currently propping up the Championship and have the joint-worst defence in the division, along with Barnsley and Scunthorpe.
Injuries to Benin international Reda Johnson and Wales Under-21 left-back Darcy Blake, on loan from Cardiff, have been a contributing factor, so boss Paul Sturrock is delighted to have added Lowry to his squad.
"Defensively, we are very short and we need to make sure we have players coming in," Sturrock told Argyle's official website.
"Shane has got real potential and he wants to do well."
Lowry was born in Perth, Australia, and recently chose to pursue a senior international career with the Socceroos, despite having played Under-21 football for the Republic of Ireland.
The Pilgrims already have two Irish youngsters on loan at Home Park - Blackburn winger Alan Judge and Celtic forward Cillian Sheridan.
Sturrock added: "He has played with Alan and Cillian in the Republic of Ireland Under-21 side, and they have waxed lyrical about him.
"Our scouts have also given us some very good reports, so he is a welcome addition."
Lowry could make his debut on Saturday, with Argyle facing a tough test against Newcastle at St James' Park.