Last January, it was revealed that AMC was already thinking about potential storylines for another season. It wasn't explicitly mentioned that the series was renewed with a third season. Now it has. Nothing specific has been revealed regarding the storyline for the upcoming third season.
The first season of The Terror is based on the novel by Dan Simmons. It takes place on a Victorian sailing ship that seems to follow a doomed course. The second season, The Terror: Infamy, focuses on an evil, shapeshifting power, which threatens the prisoners of war in a Japanese internment facility during World War 2.