Ten wedding guests were killed and another 25 were injured when their coach rolled near Greta in the Hunter Valley late on June 11.
The crash, on the bend of a highway on-ramp, occurred late at night as guests were being driven home from the wedding reception.
It was the worst road disaster in Australia for nearly 30 years.
The memorial service will be held by the state government in partnership with Cessnock and Singleton councils.
Survivors, first responders and family and friends of those involved in the fatal bus crash will come together at the Singleton Showground from 11am.
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 previously.
A ticket is not required and the event will be live-streamed 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 last month 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.
Bus driver Brett Andrew Button, 59, faces 62 charges over the crash and remains before the courts.
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