John Lithgow was born in Wanganui and educated at the Wanganui Collegiate/ He worked in stock firms for three years and farmed in New Zealand and Australia before attending Lincoln Agricultural College, where he completed a diploma in agriculture. Shortly afterwards, he joined the Agriculture Chemical Division of ICI New Zealand and, starting as a field representative in the Manawaty Wanganui area, he worked his way up to field manager for the central part of New Zealand. He was elected National Member of Parliament for Palmerston North for the 1975 term, but was defeated by the Labour candidate in 1978. Lithgow left Palmerston North two months after the 1978 election for Auckland, where he found employment. He later moved to Wanganui, where he became a Wanganui city councillor. In the 1996 election, he stood for ACT in the Whanganui electorate.

Lithgow died on 1 March 2004.