Colman was a subject of the UK genealogy programme Who Do You Think You Are? in July 2018. Although she expected that her family tree would mainly relate to Norfolk, it was discovered that her fourth great-grandfather, Richard Campbell Bazett, had been born on the island of Saint Helena and that he worked in London for the East India Company. Bazett's son, Colman's third great-grandfather Charles Bazett, married Harriot Slessor. Researchers discovered that she was born in the Indian city of Kishanganj, lost her British father when she was aged three, and then made the journey to England alone. Slessor's passage was paid for by her paternal grandmother. The episode speculated that Slessor's mother might have been Indian, but did not present concrete proof; after the episode aired, the Berkshire Record Office published the will of Slessor's mother, which proved that her name was Seraphina Donclere, evidently of European origin, and that she died in 1810.
In 2018, Colman starred as Queen Anne in Lanthimos' film The Favourite, opposite Emma Stone and Rachel Weisz. In preparation for the role, she gained 2st 7 lb (35 lb or 16 kg) in weight. For her performance, she won the Academy Award for Best Actress, the Golden Globe Award for Best Actress – Motion Picture Comedy or Musical, and the BAFTA Award for Best Actress in a Leading Role. Her awe-struck and humorous Academy Awards acceptance speech was widely covered in the media.
Colman also received positive reviews for her supporting role as Madame Thénardier in the 2018 BBC miniseries Les Misérables, an adaptation of the novel of the same name. In August 2019, she was confirmed as a guest star as Lily in the thirty-second season of the animated comedy series The Simpsons.