[1] Sibraa's father worked as a schoolteacher in country New South Wales and he moved frequently as a child, attending schools at Condobolin, Ungarie, Shortland and Newcastle.
[1] Sibraa left school after completing his Intermediate Certificate and subsequently worked as a clerk at the Metropolitan Water Sewerage and Drainage Board and at Manly Municipal Council.
[1] Sibraa joined the ALP in 1960 as a member of its Narrabeen branch and first stood for parliament at the 1966 federal election, standing unsuccessfully for the safe Liberal seat of Wentworth.
He subsequently began working full-time for the ALP, including as a paid organiser (1969–1971), administrative officer (1971–1973), and assistant general secretary (1973–1975).
He was active in the Labor Right faction associated with state president John Ducker and federal MP Paul Keating.