The England U-21 star has made 11 appearances for Leeds since arriving in August, having struggled for first-team opportunities at Highbury.
United caretaker manager Eddie Gray has agreed a deal to keep Pennant until just before Christmas.
The 20-year-old was due back at Arsenal next week, however he will now be available for Leeds' upcoming clashes against Bolton Wanderers, Charlton Athletic, Chelsea and Fulham.
His only Premiership start for the Gunners came at the end of last season, with him scoring a hat-trick in the 6-1 mauling of Southampton at Highbury.