2016–present: wider recognition
In 2016, Lawther played the main character Kenny in "Shut Up and Dance", an episode from series three of the British science fiction anthology series Black Mirror. While the episode overall received mixed reviews, he received universal acclaim and significant recognition for his performance. He also performed in the mockumentary film Carnage, directed by his frequent collaborator, comedian Simon Amstell.
In 2017, Lawther played Tibby Schlegel in Howards End, a BBC One adaptation of the E.M. Forster novel that starred Hayley Atwell, as well as the lead role of Billy Bloom in Trudie Styler's Freak Show, where he was supported by Bette Midler, Abigail Breslin, AnnaSophia Robb, Lorraine Toussaint and Larry Pine. Freak Show marked his first (and thus far only) appearance in an American film.
Later that same year, he also starred, alongside Jessica Barden, as James in the Peabody Award-winning television series The End of the F***ing World. The role also brought Lawther more acclaim from critics and further raised his profile in the entertainment industry. He would go on to reprise this role during the show's second and final season, which received a BAFTA Award for Best Drama. He also originated the role of Sam in the Stephen Daltry-directed play The Jungle, which focused on the refugee crisis in Calais, in both its London and New York productions. Lawther spent time in France meeting with refugees for this job, and ultimately found it to be one of his most challenging roles due to his character's right-wing views which were antithetical to his own. Subsequently, Lawther played the lead role of Amberson in Toby MacDonald's debut film Old Boys, as well as a supporting role in the horror film Ghost Stories.
In 2020, Lawther played the lead role in Régis Roinsard's thriller, Les Traducteurs (The Translators), his first non-English language film. As a result of fans of both Lawther and English singer-songwriter Declan McKenna frequently pointing out their resemblance, Lawther made an appearance in the music video for McKenna's song "The Key to Life on Earth". In 2021, Lawther appeared in Ridley Scott's The Last Duel, Wes Anderson's The French Dispatch, and Lucile Hadzihalilovic's Earwig. He starred as Ariel in a French production of Shakespeare's The Tempest at Les Bouffes du Nord directed by Peter Brook and Marie-Hélène Estienne and replaced Andrew Scott in the titular role of Hamlet when Robert Icke's adaptation was brought to New York City, after previously being delayed due to the COVID-19 pandemic. He appeared in the Star Wars spin-off series Andor as rebel operative Karis Nemik. In 2022 he provided the voice of Abacus Woodlouse in Aardman Animations' Lloyd of the Flies and in 2023 he also voiced of Bird-Bee and Mr. Beak-Bee in Adventures of ArachnoFly, Lloyd of the Flies' spin-off.