Lynch was born in Melbourne and worked as a schoolteacher and management consultant before entering politics. He was elected to parliament at the 1966 federal election. Lynch was appointed to cabinet at the age of 34, and served as Minister for the Army (1968–1969), Minister for Immigration (1969–1971), and Minister for Labour and National Service (1971–1972) under John Gorton and William McMahon. He was elected deputy leader of the Liberal Party in 1972, serving first under Billy Snedden and later under Malcolm Fraser. Lynch became Treasurer when the Liberals returned to power in 1975, but had to resign after two years due to a perceived conflict of interest. He was then Minister for Industry and Commerce until his retirement due to ill health in 1982. He died of cancer a few years later, aged 50.