The state government will hold the memorial in partnership with Cessnock and Singleton councils.
Ten people were killed when the bus they were travelling in rolled near Greta in the Hunter region on June 11.
Another 25 people were injured in the incident, which took place late at night as guests were being driven home from a wedding reception.
It was the worst road disaster in Australia for nearly 30 years.
The bus driver, Brett Andrew Button, faces 62 charges over the crash and remains before the courts.
The memorial service will be an opportunity to bring together those affected by the accident, including family and friends of people who died, as well as survivors and first responders.
It will be held at the Singleton Showground on October 21 and community members are being encouraged to attend to show support and solidarity.
Premier Chris Minns said the memorial would be an opportunity for people to come together to grieve, support one another and pay tribute to those affected by the "unimaginable" tragedy.
"It also provides an opportunity to recognise the courage and resilience of the frontline emergency service workers who attended the scene and treated patients in our hospitals," he said.
A ticket is not required and the event will be livestreamed on the NSW government website.
Following the service, the showground will host a free communal barbecue in partnership with local charitable organisations.
The Hunter Valley Bus Tragedy Fund, administered by Rotary, closed on Monday after raising close to $1.5 million.
The NSW government donated $100,000 and the funds raised are expected to assist those affected by the crash.
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