A private family funeral will be held afterwards.
Wellington Mayor Justin Lester said the service will be held at the Michael Fowler Centre, starting at 1pm on Friday, October 28.
The service will give the community a chance to remember "a great fighter, a great campaigner for workers' rights, a great Wellingtonian", Lester said.
"Helen Kelly was an outstanding woman. She always fought on behalf of people who needed a voice, was hugely principled, always put other people's interests ahead of her own and never compromised on her convictions."
The service is being organised by the Council of Trade Unions and Wellington City Council following consultation with Kelly's family.
Friends and family are expected to travel from all over the world to pay their respects to Kelly, who was yesterday remembered as a champion for workers rights, best known for going head-to-head with the Government over the employment status of film workers on The Hobbit and taking on Pike River Mine bosses in the wake of the disaster that killed 29 people.
Kelly has family in the UK, and a CTU spokewoman said the funeral service was arranged for the end of the month to allow family and friends overseas plenty of time to travel to New Zealand, as well as to ensure an appropriate venue was available.
Kelly was diagnosed with terminal cancer in February last year. She stood down from her role at the CTU in October 2015, and continued to campaign through the media and social media about conditions for farm and forestry workers from her bed in Wellington's Mary Potter Hospice.
She also became an outspoken advocate for the legalisation of medical marijuana.
Kelly was yesterday remembered as a "relentless changemaker" who made New Zealand a better place, by CTU president Richard Wagstaff.
Former Prime Minister and head of the United Nations Development Programme Helen Clark said Kelly was "a lifelong and very effective advocate for workers' rights".
