The drama was renewed for two more seasons last week and Nevins told Deadline that the storylines were the main consideration.
"The biggest question was, 'What is the trajectory of the show creatively?'" Nevins said.
"And after speaking with [executive producers] John Goldwyn, Sara Colleton and Scott Buck, it became pretty clear that there was a very clear three-year trajectory."
Nevins confirmed that the arc includes the current sixth season as well as the seventh and eighth runs.
"I'm not going to say with absolute certainty that this is the end," he said. "But that is the likely scenario, that the series is moving towards a definite end."
Production for the seventh season of Dexter will begin next year. The show airs on Sundays at 9pm on Showtime.
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