One of the WA Government's top spin doctors has resigned after being suspended over his behaviour at a staff Christmas party just days ago.

Stephen Kaless, a senior media adviser to Treasurer Ben Wyatt, resigned on Monday morning after the Department of Premier and Cabinet began investigating the incident.

"The Department of Premier and Cabinet was made aware of an incident at a staff Christmas function on Friday evening," a McGowan Government spokesman said.

"The staff member involved was suspended indefinitely.

"That employee subsequently tendered his resignation this morning."

Mr Kaless has been Mr Wyatt's key media adviser since Labor's 2017 election victory.

Prior to that he worked for four years as the chief of staff of the Channel 7 Perth newsroom, as listed on his LinkedIn profile.

He also previously worked as an adviser to Mark McGowan during part of his time as opposition leader, and had been a media officer for UnionsWA.

Mr Kaless has worked for both WA Premier Mark McGowan and Treasurer Ben Wyatt. ( ABC News: Andrew O'Connor )

The resignation comes at an awkward time for Mr Wyatt, who is due to hand down the Government's mid-year budget update on Wednesday.

Mr Kaless had been expected to play a central role in the Government's media messaging on the budget update.

His Twitter account has been deactivated.