Olukemi (later shortened to Kemi) Olufunto Adegoke was born on 2 January 1980 in Wimbledon, London.[11] Her mother had travelled from Nigeria to the UK to give birth in St Teresa's private hospital before the British Nationality Act 1981 abolished automatic birthright citizenship for those born in the United Kingdom, and then returned to Nigeria shortly after Badenoch was born.[12][13][14]In later interviews, Badenoch denied claims she was an "anchor baby" and asserted that her family did not know she was in fact eligible for a British passport until she was a teenager.[15][16] She is one of three children born to Nigerian Yoruba parents.
Her father, Femi Adegoke, was a GP who later founded a publishing company in Nigeria and became an activist for the rights for the Yoruba people. Her mother Feyi was a professor of physiology in America and at the University of Lagos. She has a brother and a sister.[17][18] According to a profile in The Times, Badenoch is the first cousin once removed of former Nigerian Vice-President Yemi Osinbajo.[19]
Badenoch spent her childhood living in Lagos, Nigeria, and in the United States, where her mother lectured.[20][21] Badenoch has spoken about having a "very tough upbringing" in Nigeria. Her family lived in the middle class neighbourhood of Surulere and she was a student at the private International School of Lagos. Badenoch has described her background as "middle-class" but said in 2018 "Being middle class in Nigeria still meant having no running water or electricity, sometimes taking your own chair to school" and claimed that her family went through "periods of poverty" due to inflation.[22] She returned to the UK at the age of 16 to live with a friend of her mother's owing to the deteriorating political and economic situation in Nigeria, which had affected her family.[23] During her parliamentary maiden speech Badenoch stated that she was "to all intents and purposes a first-generation immigrant".[24]