The crime drama starring Timothy Olyphant as Deputy US Marshal Raylan Givens has been ordered for 13 further episodes by FX Prods and Sony Pictures Television.
The show's current third season is averaging 4.3 million viewers each week, marking an 8% rise from its previous run. There are six episodes still to air on the network.
"Justified is one of television's best series and this season has reinforced that excellence," said FX's original programming executive Nick Grad. "We look forward to many more seasons to come."
The series is based on Fire in the Hole and other novels from author Elmore Leonard.
Sons of Anarchy star Adam Arkin recently signed up to appear in Justified.
> Justified exec hints at character death