The 21-year-old, who cannot be named for legal reasons, on Tuesday pleaded guilty in the Victorian County Court to two charges of possessing explosive substances without lawful excuse.
The United States' Federal Bureau of Intelligence first tipped off Victorian detectives in February 2024 after the man posted on social media, claiming he would kill people who were bullying him.
A search warrant at his home uncovered rounds of ammunition and substances, including potassium nitrate and red phosphorus.
The man was charged and bailed but arrested again in September 2024 after he purchased more chemicals online.
The substances were located at another search of his home, alongside walkie-talkies, tactical vests, a gas mask and safety goggles.
The man's notebooks were also analysed and revealed messages in code, referencing plans for a school shooting and mass violence incidents in Melbourne.
But he was unlikely to act out his thoughts, forensic clinical psychologist Michael Davis told the court.
He said the man's violent fantasies were a symptom of his diagnosed schizotypal personality disorder, characterised by deficits in social and interpersonal skills.
"He wants some friends and he's never been able to make that happen because of how eccentric and unusual he is," Dr Davis said.
"He doesn't take it out on people physically. He just writes about taking revenge."
The man's fixation on chemistry and substances was also a symptom of his autism spectrum disorder, Dr Davis said.
The man was not overtly psychopathic but he could have a short-term psychotic episode if he was not treated and remained in isolation with his thoughts, the psychologist said.
Defence lawyer Glenn Cooper argued the man's 22 months in prison have been very onerous due to his mental health conditions, isolation in custody and young age.
The man had offered to plead guilty to the charges in May 2025 but prosecutors only accepted the plea deal in July, Mr Cooper said.
Judge Douglas Trapnell criticised the delays and said it was clear the man had done enough time.
He told the prosecution the case should have been settled "ages ago".
"By dithering around at this as long as you have, you have taken it out of my hands," the judge told the prosecutor.
"This young man with no prior convictions has been languishing in detention."
The man's ongoing treatment with a psychiatrist would have to be voluntary because any further therapeutic order would amount to additional punishment, Judge Trapnell said.
The judge then abruptly proceeded to convict and discharge the man of the two offences, meaning the 21-year-old will be released from custody later on Tuesday.
The judge will hand down his reasons for sentence at a later date.
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