Her father's upper-class British ancestors lived in several countries during the height of colonialism and the British Empire, including Peking, China (where her paternal grandfather was born), Calcutta and Bombay, India, Cairo, Egypt, and Tasmania, Australia (one of her paternal great-great-grandfathers, Henry Arthur Blake, was Governor of Hong Kong).[2] Wilde's father's ancestors include abolitionist and Anglican minister James Ramsay, politician George Arbuthnot, lawyer, judge, and literary figure Henry Cockburn, Lord Cockburn, Lord Provost of Edinburgh Sir William Arbuthnot, 1st Baronet, and Sir Thomas Osborne, 9th Baronet. Wilde's ancestry consists of English, Scottish, Irish, and German; she is also of more distant Sephardi Jewish descent from a paternal ancestor, Ralph Bernal (1783–1854), a British Whig politician and actor.
Wilde has said that as a result of her parents' occupations, she has a "strong journalistic streak", being "really critical and analytical". Both her parents were prominent in the Washington social scene, hosting dinner parties. Her mother once recounted a story of a four-year-old[6] Wilde eavesdropping one night on a conversation between diplomat Richard Holbrooke and singer Mick Jagger, until Jagger noticed her and shooed her to bed. She has wanted to become an actress since the age of two. For a short time, Wilde's family had a house in Guilford, Vermont. She attended Georgetown Day School in Washington, D.C., as well as Phillips Academy in Andover, Massachusetts, graduating in 2002. She also studied acting at the Gaitey School of Acting in Dublin, Ireland.