Devlin revealed that the TNT con-man drama's fifth season finale - which airs on December 25 - was written as a potential series finale in an open letter to fan site LeverageFans.com.
"As of the writing of this letter, we still do not know if there will be a season six of our show," Devlin wrote. "Just as we didn't know when we created the last three episodes which are about to air. Because of this uncertainty, [co-creator] John Rogers and I decided to end this season with the episode we had planned to make to end the series, way back when we shot the pilot.
"So, the episode that will air on Christmas is, in fact, the series finale we had always envisioned."
However, Devlin insisted that the possibility of a sixth season remains should TNT decide to renew Leverage for another year.
"Everyone involved with the show, from the cast, the crew, the writers and producers, would like nothing more than to continue telling these stories," he continued. "But, in case we do not get that opportunity we felt that, creatively, after 77 episodes, we owed it to you, our fans, to end the show properly.
"I sincerely hope you watch these last three episodes. They build to our conclusion. And the finale, I believe, is the most powerful episode we've ever done."
Leverage is the only remaining TNT drama yet to receive a pick-up - the cable network previously renewed its shows Rizzoli & Isles, Major Crimes and Franklin & Bash.
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Watch Leverage star Gina Bellman talk season five with Digital Spy below: