Deadline reports Harington is set to star in an upcoming film in the MCU. The specific franchise is unknown at this time, but with Disney's D23 Expo taking place this weekend, an official announcement could be scheduled.
Of course, President Kevin Feige and Marvel Studios has a number of different projects in different stages of development. Comic-Con International in San Diego saw Marvel Studios announce 11 new upcoming projects across the big screen and the Disney+ streaming service: Black Widow, The Falcon and Winter Soldier, Eternals, Shang-Chi: The Legend of the Ten Rings, WandaVision, Doctor Strange in the Multiverse of Madness, Loki, What If?, Hawkeye, Thor: Love and Thunder and Blade.
If the report turns out to be true and Harington is joining an MCU film, we can probably eliminate Black Widow and Eternals since both are in different stages of filming. The main cast of Eternals was revealed at Comic-Con International, and it's more likely Marvel Studios would want Harington to have a starring role in a feature film.
One possibility is Harington will star in a film that is yet to be announced. There are rumors Marvel may look to bring Namor the Submariner to the MCU, though the details behind his film rights remain complicated.
Harington starred as Jon Snow on HBO's Game of Thrones for eight seasons, from 2011 to 2019.