The one-time State of Origin player and former Knights captain was handed a three-year community corrections order in Wollongong Local Court on Wednesday after he confessed to buying 39 grams of cocaine - 13 times the trafficable quantity - from a dealer at a home in Cameron Park in November 2018.

He will be required to perform 300 hours of unpaid community service work as part of his sentence.

Mullen, 32, told police he had been in the grip of his own daily cocaine habit after the downfall of his rugby league career when he purchased the drugs, which he planned to on-sell to friends.

"Just ever since my career finished, I spiralled out of control and was taking cocaine on a daily basis just to get through the day, to suppress the demons, I suppose," Mullen said.

"And a lot of prescription drugs, stuff which led me to rehab ... well I did go through a dark stage, yeah."

Defence lawyer, Paul McGirr, described Mullen's situation as "extremely sad" for "one of Newcastle's favourite sons".

"No one who takes cocaine ... ever says their life has improved since they used cocaine," he said.

"He has had a very big fall from grace, he's hit rock bottom, [but] he's well and truly on the road to recovery.

"I have confidence we won't see him darken the doors of the courtroom again."

He said Mullen had had dreams of playing in the NRL again.

The court heard Mullens' dire addiction reached fever pitch when he overdosed less in early December 2018. He was found unconscious on his parents' couch and rushed to hospital.

He subsequently entered a rehabilitation program and says he has been clean ever since.

He was arrested in May 2019, less than a month after moving to the Illawarra to live with his girlfriend, who is due to give birth to their first child next week. She supported him in court on Wednesday, along with his mother.

A set of agreed facts reveal Newcastle police began investigating one of Mullen's up-line suppliers in August 2018 over drug import allegations.

They discovered the man had imported, and planned to further import, cocaine, MDMA, Xanax, Ketamine, pseudoephedrine and butanediol, which he had delivered each time to one of 10 PO boxes registered in fake names.

Covert surveillance carried out by detectives revealed Mullen to be in regular contact with the supplier, both at his home address and via telephone.

The pair are recorded discussing quantities and prices of the cocaine, which they referred to as "rack".

Mullen later admitted to buying the 39 grams of cocaine in four separate transactions between November 23 and November 30. The estimated street value of the drugs is $12,000.

He told police he mainly sold to friends using encrypted apps such as WhatsApp and Wikr to avoid police detection.

He also said he used code words in the messages to further conceal his deals.

In sparing Mullen a jail sentence, Magistrate Jillian Kiely noted he had undergone extensive rehabilitation and she did not consider the matter had reached the threshold for a term of imprisonment.

"Not only has he personally and professionally hit rock bottom, he almost died of an accidental overdose and now suffers from permanent hearing loss," she said.

"That would have served as an extreme wake up call."