The 25-year-old, who scored 46 goals for the Gulls between 2007 and 2011, joined up with his team-mates on Monday and will be available for the clash with Rotherham at Plainmoor on Tuesday night.
The two clubs have also agreed an option to extend the loan deal for the forward, who left Torquay for Swindon two years ago, until the end of the season.
Benyon found his chances restricted at the County Ground and after a brief spell with Wycombe he made the permanent move to Southend 13 months ago.
But he made just 12 starts for Paul Sturrock's men before a return to Devon.
