Voters in the federal seat of Canning will have the chance to elect a new member with a by-election for the seat to be held on September 19.

The by-election was triggered by the death of Liberal MP Don Randall last month from a heart attack.

It is expected to act as a litmus test for the Abbott Government, which is currently lagging behind Labor in opinion polls.

SAS soldier Andrew Hastie, 32, is expected to run for the Liberal Party after being recommended by the party's selection committee as the best of seven candidates to nominate.

It is understood he had the support of influential Liberals including Finance Minister Mathias Cormann.

Labor is yet to choose a candidate, but lawyer Matt Keogh is widely tipped to get the nomination.

The seat is considered a Liberal stronghold, with Mr Randall holding it with a margin of almost 12 per cent.

Nominations close next Thursday.