Brought up in the settled Romani community, in west London, Hancock’s family emigrated to Canada to seek a better life, in 1955. As a young man, he dropped out of school to return to England, where he undertook various jobs and became fascinated by the West African Creole of immigrant friends, because of its structural resemblance to the mixed English-Romani dialect.
A study of Sierra Leone Creole he wrote, led to him being accepted as a mature student, to do first a diploma then a PhD at the University of London. During this time, he wrote about English Romani, for the Journal of the Gypsy Lore Society and was invited to speak at the academic conference that accompanied the First World Romani Conference. There he met Vanya de Gila Kochanowski and Matéo Maximoff, the first other published Roma writers he had met. Recruited by the University of Texas at Austin in 1972, he became an internationally renowned Creole Studies expert.
After he had been given tenure as a professor, he publicly revealed his Romani ethnicity. He served a term as International Romani Union representative at the United Nations and served as a member of the US Holocaust Memorial Council under President Bill Clinton.
Widely influential in the international Roma Civil Rights movement, he has published more than 300 books and articles on the Romani people and language (particularly the Vlax dialect) and has established one of the largest archives of books and papers on the Roma.