Brodie Jake Dewar, 20, is facing a manslaughter charge after allegedly attacking Mr Picton, 36, in Northbridge, in Perth's inner city, in the early hours of December 27.
He was also accused of causing bodily harm over an incident in the Perth suburb of Kalamunda on December 25 shortly after midnight, when he allegedly punched another man to the ground outside a pub.
Dewar, who is on bail, pleaded guilty on Wednesday in Armadale Magistrates Court to the lesser charge of assault occasioning bodily harm over the incident.
A Perth court previously heard Dewar knocked the man in his 40s unconscious after an incident involving the younger man's sister.
Dewar then recorded the man lying on the ground with his mobile phone and said "don't hit on my sister" and "bro, keep snoring", the court was told.
Dewar then used the heavily intoxicated man's phone to call him an Uber after his friends helped him.Â
The man suffered minor injuries and later told police he didn't remember the incident, which was recorded on CCTV.
Dewar is scheduled to reappear in Armadale Court for sentencing on May 6.
He is scheduled to appear in Stirling Gardens Magistrates Court on April 29 on the manslaughter charge relating to Mr Picton's death.
Mr Picton, who has been lauded as a brilliant political tactician, died in hospital several weeks after hitting his head on the pavement during the incident with Dewar.
His death triggered an outpouring of grief from his family, friends and colleagues, as tributes flowed from the prime minister, several premiers and business leaders.
Mr Picton had advised state and federal politicians, and helped guide WA Labor to a landslide 2021 election victory.
A Perth court has previously heard Mr Picton was ejected from the Paramount Nightclub due to intoxication.
He had repeatedly grabbed Dewar's 18-year-old cousin around the waist and made unwanted advances towards her, defence lawyer Simon Watters has previously told the court.
The young woman, Dewar and others in their group repeatedly told Mr Picton to stop and go away, but the unwanted attention continued, the court heard.
Dewar allegedly struck Mr Picton's face outside a fast-food restaurant and he fell to the ground, hitting his head.
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