A Brisbane councillor has been chosen over a current Turnbull government assistant minister to stand in a west Brisbane seat at the next federal election.

Walter Taylor Ward councillor Julian Simmonds has been picked instead of Assistant Minister for Social Services and Disability Services Jane Prentice to run in the seat of Ryan at the next election.

Cr Simmonds' preselection meant a council byelection would have to be called, should he be successful, if the federal election is called more than a year before the scheduled 2020 council election.

Otherwise, Cr Simmonds' seat in council could be treated as a casual vacancy, with his successor appointed by the LNP.