The son of Kenneth Munro Gibb Kennett (1921–2007), and Wendy Anne Kennett (1925–2006), née Fanning, he was born in Melbourne on 2 March 1948. He attended Scotch College; and, although an unexceptional student academically, he did well in the school's Cadet Corps Unit. He also played football (on the wing) for the school. His failure to rise above the middle band academically almost led him to quit school in Fourth Form (Year 10 – 1963), but he was persuaded to stay on. His Fifth and Sixth Forms were an improvement, but he was still described in school reports as "confident and at times helpful boy. Sometimes irritates. Sometimes works hard" (1964), and "[a keen, pleasant, though sometimes erratic boy" (1965).