The by-election in Johnston is being held due to the resignation of Ken Vowles, who has held the seat for Labor since 2012. Vowles was a senior planner with Parks and Wildlife before entering parliament, and is a former captain of the Northern Territory cricket team. He served in the ministry after the 2016 election, but was sacked in December 2018 after failing to declare confidence in Chief Minister Michael Gunner, then ejected from caucus together with backbenchers Jeff Collins and Scott McConnell. The campaign received national attention a fortnight out from polling day when the Greens published a how-to-vote card that had Labor in last position, in protest at the government's lifting of a moratorium it imposed on gas fracking exploration shortly after coming to office in 2016.
Johnston covers the northern Darwin suburbs of Millner, Jingili and Moil, most of which was covered prior by the seat of Jingili before 2001, when northern Darwin was decisively dominated by the CLP. Jingili was held from 1974 to 1984 was Paul Everingham, the Northern Territory's first Chief Minister and a future member of the House of Representatives. Chris Burns won Johnston for Labor as part of the 2001 election victory, and served in the Martin/Henderson ministry through to his retirement in 2012. The seat then passed to Ken Vowles, who retained the seat with a comfortable 5.7% margin despite Labor's defeat in 2012, then added 8.1% to his margin in the landslide of 2016.
Labor's candidate is Joel Bowden, general secretary of Unions NT and a former AFL player for Richmond. The Country Liberal Party candidate is Josh Thomas, a drug and alcohol outreach worker and blues guitarist. Former Chief Minister Terry Mills' CLP breakaway party, the Territory Alliance, has endorsed Steven Klose, who has worked in event management and marketing and communications. Also in an unusually large field of seven candidates are Aiya Goodrich Carttling, a children's entertainer, for the Greens; Braedon Earley, a former president of the Country Liberal Party who broke away to form the 1 Territory party at the 2016 election, and is now running under the banner of Ban Fracking Fix Crime Protect Water Party; and two independents, Trevor Jenkins and George Mamouzellos.