The families of the two Sydney siege victims, as well as the survivors, have been invited to a twilight ceremony marking one year since a gunman took them hostage in Martin Place.

For 16 hours on December 15, 2014, gunman Man Haron Monis terrorised 17 people whom he had taken hostage inside the Lindt cafe.

The siege ended in the early hours of the next morning, and when police stormed the building after hearing gunfire Monis had already shot cafe manager Tori Johnson dead.

He was 34 years old.

Barrister Katrina Dawson, 38, was killed in the crossfire along with Monis.

The public ceremony will be held at twilight on Tuesday, December 15 in Martin Place.

"This is an important opportunity to mark one year since the traumatic events of the Martin Place siege," Premier Mike Baird said.

"It will be an understated public ceremony to remember victims and survivors, and to recognise the response and resilience of a community that refused, and refuses yet, to be divided by those who wish to cause harm."

The ceremony will involve light projections that incorporate images of the floral tribute laid at the site.

Five nights of light projections onto the Lindt cafe building will follow.

The ceremony will be held at 8.15pm.