Timothy Raymond Mathieson, 66, appeared remotely in Melbourne Magistrates Court on Thursday, by video link from his lawyer's office.
The court was told Mathieson was initially facing three charges.
Mathieson sat behind his barrister Brad Penno, who said the matter had resolved and his client will plead guilty to one sexual assault charge.
The other two charges were withdrawn on Thursday, and further details of those offences were not aired in court.
Mr Penno asked for Mathieson to be handed a diversion, which would mean he escapes a criminal conviction and has the case diverted out of the justice system.
The prosecution asked for two weeks to assess whether a diversion would be appropriate.
Mathieson will return to the court on August 31 for a further mention.
He was in a relationship with Ms Gillard for more than 10 years, after meeting when he was a hairdresser but split in 2020.
The couple lived together at the The Lodge and Kirribilli House throughout her three-year term as prime minister.
He was colloquially known as the 'first bloke', a reference to the tradition of the wives of US presidents being called first ladies.
17°C