At the time the now 48-year-old Gold Coast solicitor was under surveillance by Queensland's corruption watchdog.
MacCallum, a lawyer for more than 20 years, was later charged with money laundering and fraud as well as drug offences but pleaded guilty only to five cocaine possession charges in a Brisbane court on Monday after the other charges were discontinued.
The first offence occurred in January 2020 when detectives recorded MacCallum getting drugs from a man at Varsity Lakes.
About two months later MacCallum's partner admitted she "secreted drugs" on her body during a police welfare check.
She had wrapped herself in a towel so officers let her go to the bathroom where she flushed substances - that she said belonged to MacCallum - down the toilet, prosecutor Brendan White said.
After a client was sentenced to jail for cocaine possession but immediately released on parole in the Brisbane Supreme Court on May 18, 2020, MacCallum drove the man to the Gold Coast.
Detectives recorded them discussing cocaine and the client arranging collection of 3.5g of the drug.
The pair discussed the texture, amount and purity of the cocaine the client got while MacCallum waited in the car.
"We'll enjoy the trip to Labrador - nose is ready," the client said, before supplying MacCallum a line of cocaine that was consumed in the vehicle.
MacCallum was charged after police found cocaine at his Broadbeach property on July 6, 2020.
The lawyer had obtained significant professional help for untreated PTSD and ADHD since his arrest and rehabilitated from what was described as regular weekend cocaine use, Mr White said.
He was also remorseful, apologetic and deeply ashamed of his conduct and its impact on his family, defence barrister Patrick McCafferty KC told the court.
Having a line of cocaine with a client demonstrated an appalling lack of judgment.
"But it must be seen in the context of a person who had an addiction issue."
Brisbane Chief Magistrate Janelle Brassington found it highly unlikely MacCallum, who risked everything he built over the years including his reputation, would offend again.
She found his mental impairment led to the use of cocaine to mask or manage increasing symptoms of PTSD and ADHD.
Regarding the use of cocaine after leaving court, Ms Brassington said MacCallum would be under no illusions about his client's parole conditions.
"It is conduct that can seriously impact the community's confidence in the system of justice and conduct likely to undermine the public's trust."
At the time MacCallum was a law firm principal, conducting his practice and making decisions of serious import to himself, clients, staff and the community.
Ms Brassington sentenced MacCallum to three months behind bars, fully suspended for 12 months for the one possession charge, for which a conviction will be recorded.
She fined him $2500 for the remaining four charges.
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