He was a member of the House of Representatives from 1987 to 1996, holding the Queensland seat of Petrie for the Australian Labor Party (ALP).

[1] He is the youngest of four sons born to Doris (née Thompson) and Claude Johns; his father was a painter and decorator.

From 2002 to 2004, he was appointed Associate Commissioner of the Commonwealth Productivity Commission, an Australian government policy research and advisory body,[5] with the responsibility for an inquiry into the national workers' compensation and occupational health and safety framework.

His latest book is The Burden of Culture In 2017, Johns was appointed by the Turnbull government as the commissioner of the Australian Charities and Not-for-profits Commission.

In 2023, Johns was chairman of Recognise a Better Way, a group arguing the "No" case regarding the Albanese government's proposal for Indigenous Voice to Parliament.