March 10 likely for Cottesloe by-election

Former WA premier Colin Barnett has officially resigned from the seat of Cottesloe and a Liberal spokesman says a by-election is likely to be held on March 10.

The spokesman told AAP the ex-premier had formally resigned on Friday, having previously announced in December his plans to retire.

However, a WA Electoral Commission spokesman said no writ had yet been officially received.

Mr Barnett stayed on in parliament after a landslide election loss in March that ended his Liberal-National government's eight years in power.

Labor previously announced it would not contest the by-election, conceding it would not win the safe Liberal seat.

Candidates for the by-election include mining executive Emma Roberts, real estate agent Deborah Brady, Cambridge councillor Andres Timmermanis, marketing director Sandra Brewer and Kwinana Industries Council president David Honey.

Mr Barnett will leave behind a career as WA's second-longest serving post-war premier, including major infrastructure projects such as Elizabeth Quay and Optus Stadium.

The 67-year-old has continued to comment publicly since his move to the back bench, criticising the new Labor government and his own government, most notably saying his second cabinet was weaker than the first.