He hails from the village of Kasavu in the province of Naitasiri and his mother is from the village of Qarani, Gau in the Lomaiviti group.
Kadavu Province is one of fourteen provinces of Fiji, and forms part of the Eastern Division, which also includes the provinces of Lau, Lomaiviti and Rotuma.
He was a scion of the chiefly clan of the Tui Nairai or paramount chief of Nairai island in the Lomaiviti Group.
The Lovoni people, being an independent kingdom with several strategic tributaries, ensured their role as mercenaries of war in the central Fijian province of Lomaiviti, which at the time of European contact, was undergoing a major power struggle between the Noble Houses of Verata and their ally and kin the House of the Roko Tui Bau and the rising power of the Vunivalu of Bau.
A native of Moturiki Island in the Lomaiviti archipelago, Siwatibau was married to the late academic leader and former Vice-Chancellor of the University of the South Pacific, Savenaca Siwatibau, from 1966 till his death in 2003.