Stephen Kaless, the former senior media advisor to WA Treasurer Ben Wyatt, has been charged with the indecent assault of a woman in her 20s at a work Christmas party, the ABC understands.

Key points: Mr Kaless worked for both Mr Wyatt and Premier Mark McGowan

Mr Kaless worked for both Mr Wyatt and Premier Mark McGowan He allegedly assaulted the woman at a Perth bar and resigned soon after

He allegedly assaulted the woman at a Perth bar and resigned soon after Mr Kaless was previously the chief of staff of the Channel 7 Perth newsroom

Mr Kaless resigned last month from his post as one of Mr Wyatt's most senior staff after a complaint about his behaviour at the party, which took place at a Perth bar on Friday December 13.

Before quitting he had been "suspended indefinitely" from his position.

The scandal came just days before Mr Wyatt handed down the WA Government's mid-year budget update.

Mr Kaless worked for Channel 7's Perth newsroom for four years before joining Mr Wyatt's office. ( Facebook: Stephen Kaless )

WA Police confirmed a 44-year-old man from Bayswater, who the ABC understands is Mr Kaless, had been charged with indecent assault over the incident.

Mr Kaless allegedly assaulted the woman, a colleague aged in her 20s who was known to him, while they were in a bar area of the hotel.

The Kaless scandal rocked WA Treasurer Ben Wyatt's office a day out from handing down the mid-year economic review. ( ABC News: James Carmody )

Mr Kaless had 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 Mr McGowan during his time as opposition leader and had been a media officer for UnionsWA.

Stephen Kaless (right) was a top media adviser to Mark McGowan in opposition. ( ABC News )

Mr Kaless is due to appear in the Perth Magistrates Court on January 29.