The sixth season of the American ABC fantasy-drama series Once Upon a Time was ordered on March 3, 2016. It premiered on September 25, 2016, and concluded on May 14, 2017. The season is the last to feature the series' main storyline, with the seventh season seeing a soft reboot. Due to this, original cast members Ginnifer Goodwin, Jennifer Morrison, Josh Dallas and Jared S. Gilmore, as well as long-time cast members Emilie de Ravin and Rebecca Mader, all departed as series regulars after the season; all would make at least one appearance the following season.

Once Upon a Time is an American fantasy adventure drama television series that aired for seven seasons on ABC from October 23, 2011, to May 18, 2018. The action alternates between two main settings: a fantastical world where fairy tales happen, and a fictional seaside town in Maine called Storybrooke. The "real-world" part of the story unfolds with the characters of Emma Swan and her 10-year-old son, Henry Mills. Henry discovers the other people of the town are fairy-tale characters. The audience is shown the backstory of the town's people as fairy-tale characters, in conjunction with their unfolding stories in the "real-world". In the seventh and final season, the "real-world" portion of the story takes place in Seattle, Washington, in the fictitious neighborhood of "Hyperion Heights", with a new main narrative led by adult Henry, and his wife and daughter.