Geoffrey Lehmann was born in Sydney at the Crown Street Hospital and spent his early childhood at Mcmahon's Point on Sydney Harbour. He was educated at the Shore School. His family background acknowledges mixed Irish and German descent and Lehmann studied German literature at university. Lehmann graduated in arts and law from the University of Sydney in 1960 and 1963 respectively. While at university he co-edited with Les Murray the magazines Arna and Hermes and, during this period, was associated with the Sydney Push. Lehmann has practised as a solicitor, becoming a partner with C. R. Willcox, and lectured in law and taxation at the University of New South Wales. He later became a partner in the international accounting firm PriceWaterhouseCoopers. He has written occasionally on taxation for the Australian Financial Review, describing himself as 'a tax consultant and poet', and has held the position of Chair of the Australian Tax Research Foundation.
Lehmann's first volume of poetry was The Ilex Tree (1965), a collaboration with Les Murray. Since then his poetry has been published regularly and collected in a number of widely admired volumes. Lehmann explores human nature with poems of diverse settings, including ancient Rome and rural New South Wales. The latter setting is exemplified in Ross' Poems (1978), a series that employs the voice of an Australian farmer to explore the ideas of family and community. Lehmann's Roman poetry is often seen as a metaphor for the destruction of civilization and is sometimes connected with Sydney. This view of society is balanced by Lehmann's family poetry with which he often examines the life of his father and grandfather. Lehmann has won the Grace Leven Prize three times, most recently for Collected Poems (1997). Lehmann's influences have included C. P. Cavafy and Kenneth Slessor.
In addition to his poetry, Lehmann has written a novel and edited several anthologies of Australian poetry. He has also published a book of art criticism on Australian naive painting. With Cynthia Coleman, he co-authored Taxation Law in Australia (1989).