The state apology to be delivered in Parliament aims to recognise that Vietnam veterans were not treated fairly on their return to New Zealand after the war.
The apology was agreed to earlier in a memorandum of understanding between the Government, the Ex-Vietnam Services Association and the Royal New Zealand Returned and Services Association.
Under the agreement reached in 2006, veterans exposed to Agent Orange received a $30 million package plus the apology.
Miss Clark said it took 33 years to get to this point for complex reasons.
"It's an irony that it's waited until my generation to do it. The guys who went away to Vietnam are a little bit older than I am and I didn't even remember the beginning of the deployment particularly well," Miss Clark said on TV One's Breakfast programme.
"It was very controversial at home ... the men felt when they came back they were treated very differently from veterans who had been to Korea, World War 1 and 2."
As a student in the 1970s Miss Clark had opposed the war.
"We have to see that justice is done. It's a chapter of our history that we need to get closure on."
Veterans Affairs Minister Rick Barker would host a function for representatives of the veterans' community later on Wednesday afternoon.
The apology would come before commemorative events over Queen's Birthday weekend. "Tribute08" would begin on Friday with a civic welcome in Civic Square, Wellington, at 4pm.
Mr Barker said the weekend of commemorations had been organised largely by veterans with help from New Zealand Defence Force personnel.
