 Born to a Goan family in Mumbai, de Souza lived in Zanzibar before settling in Kenya in 1942.Fitz de Souza took a first degree in England and trained as a barrister at Lincoln's Inn.As a young man in 1952 he joined a team of lawyers from various Commonwealth countries, including the British barrister Denis Nowell Pritt and other lawyers educated in England but not born there, defending Kenyans accused of Mau Mau activities by the British colonial administration, in a series of trials including that of Jomo Kenyatta.