Stephen John Ellis, 48, a former journalist and senior NBN adviser, resigned from the office of then-communications minister Malcolm Turnbull after his arrest in May last year.

He previously pleaded not guilty to six charges including drug possession, offensive behaviour, carrying offensive items and committing an act of indecency in the presence of another.

A hearing on those charges, set to start this week, was abandoned after Ellis appeared in the ACT Magistrates Court on Monday and pleaded guilty to offensive behaviour and possessing a drug similar to LSD.

He also faced two fresh charges for drug offences related to the incident. Prosecutors dropped all remaining charges against Ellis, while another two related offences were dismissed.

Court documents said police were called to the airport after a member of the public reported a male acting suspiciously in the disabled public toilets near a departure gate.

They arrived to find Ellis partly dressed in a cubicle, not wearing shoes or socks.

He was later arrested and cautioned. Police searched his belongings, discovering a tab of a drug believed to be LSD, a small clip seal bag containing methylamphetamine, and four lengths of white rope in his luggage.

In a police interview, Ellis said he had no clear understanding of the circumstances surrounding the incident, but admitted he was aware his actions wouldn't be considered normal or acceptable by a reasonable person.

Ellis' lawyer, Grant Brady, SC, urged magistrate Maria Doogan not to record convictions against his client, arguing he was in the midst of a drug-induced psychosis at the time of his offending.

Mr Brady said that placed his moral culpability for his crimes at the lower end of the spectrum.

Ellis had undergone a mental health assessment the day after his arrest and had since sought help from a psychologist and psychiatrist for an adjustment disorder.

Mr Brady said his client's loss of professional standing due to the publicity surrounding his case was significant and "dramatic", and he had struggled to find full-time work after his arrest.

"What was a stellar career has gone into freefall."

Mr Brady said Ellis' record was otherwise unblemished, he was of good character and had been making a significant professional contribution in his role with the federal government at the time of his arrest.

The court heard Ellis' partner was from the United States and any criminal convictions recorded against him, especially for drug offences, could prevent Ellis from returning to the country.

Ms Doogan said she took into account Ellis' lack of criminal history, show of remorse and age, and the unusual circumstances surrounding the incident when considering his moral culpability. "What happened is just bizarre," she said.

She accepted the impact on his reputation, employment prospects and loved ones had been "very significant".

"What happened this particular day has ultimately become tragedy for you."

Ms Doogan said she would not record a conviction on either charge or make Ellis serve a good behaviour order.

She ordered he pay court costs of $73.