Napier RSA, the longest continually trading Returned and Services Association in New Zealand, celebrates its centenary on the first weekend of December.
While Christchurch has an older RSA, it was forced to close until a new building was constructed after the devastating earthquake of 2011.
"Christchurch is recognised as the oldest but they were not in operation following the earthquake. We were about the third to be established," chief executive Craig Williams said.
Being operational does not simply mean the bar is open - the RSA is the largest voluntary welfare organisation in New Zealand. Napier RSA was founded to support and assist soldiers returning from both Gallipoli and European conflicts.
Just which RSA was the second-oldest in New Zealand had been "argued for years" but Mr Williams said it looked likely Napier was third.
Events are planned over three days starting Friday December 2.
Mr Williams said a centenary dinner was being held on Saturday evening, with politicians and RSA dignitaries invited to an evening of cocktails, award presentations and live music.
He said Prime Minister John Key declined an invitation because he had prior commitments.
Other events include live music on Friday and a Greenmeadows Primary School kapa haka and music show followed by a children's party on Sunday for "our coming generation".