In 2017, he reprised his role as Jamie from 2003's "Love Actually" in the television short film "Red Nose Day Actually", by original writer and director Richard Curtis. Also that year, Firth returned as Harry Hart in the sequel "". In 2018, Firth again portrayed Harry Bright in the sequel to "Mamma Mia!", "Mamma Mia! Here We Go Again". That year, he also appeared as William Weatherall Wilkins in the musical fantasy film "Mary Poppins Returns", starring Emily Blunt in the title role. He also played British naval commander David Russell in Thomas Vinterberg's "Kursk", a film about the true story of the 2000 Kursk submarine disaster, in which he starred alongside Matthias Schoenaerts. In 2019, he had a cameo as British General Erinmore in Sam Mendes’ World War I film "1917". Set in 1947 England, Firth starred with Julie Walters in "The Secret Garden" (2020).