The 69-year-old took charge of the Tabriz-based football team until the end of the season.
Leekens resigned as his coaching post at the Tunisian club Etoile Sportive du Sahel in late November.
Tractor Sazi is his 26th coaching assignment.
Tractor Sazi is fourth in Iran Professional League behind Sepahan, Padideh and Persepolis.
Leekens replaced Welshman John Toshack who left the club in September.
He was national coach of Belgium from 1997 to 1999 and from 2010 to 2012.
In recent years he also trained Lokeren and the national teams of Tunisia, Algeria and Hungary.