"This has been a decision that I have not taken lightly and it is one that has taken me many months to make. I am leaving to pursue my goals and to grow with my family.
"I am very proud of my service with the NZDF and I am very grateful for all of the support I have received from the NZSAS and the NZDF."
Corporal Apiata grew up in the eastern Bay of Plenty at Te Kaha, where he was presented with his VC medal five years ago.
Yesterday, locals voiced their support for his life change.
His aunt Ola Paora, his mother's sister, told the Herald she was yet to meet his new partner, whom she said he had married.
Asked if the ceremony had taken place in Te Kaha, she replied: "No, it was very secret. We didn't even know until after it happened. I've never met her. As long as he's happy and she looks after him that's all that matters."
Corporal Apiata was such an unassuming person he would not have wanted a fuss, Ms Paora said.
She'd last seen her nephew at a recent tangi and had heard he might be leaving the SAS, but because it had been such an important part of his life for so long it would be strange to think of him in civvies, she said.
"There was word of it, but I myself said, 'I'll believe it when I see it'."
A Defence Force spokesman would not say whether the new relationship had influenced the soldier's decision to leave.
"It's not something we would release publicly, his marital status. He is a very private person."
The High Wire Trust works with young people in South Auckland, giving them trade training and leisure opportunities.
It has strong links with the armed forces, running an academy to help young people towards careers in the military. Other former SAS soldiers are on its staff.
Former Papakura Mayor Calum Penrose, who works with the trust, said Corporal Apiata would start next month. He would be looking after an environmental camp on the Awhitu Peninsula on Auckland's west coast and also work at its offices in Papakura.
"We're attracting people who are role models for our young people," he said.
"I think he's looking for different challenges in his life, I think he will make a huge impact on young people's lives. I'm sure he'll blossom and flourish and I think he'll touch the lives of every young kid who goes through High Wire trust."
Mr Penrose said that out of respect for Corporal Apiata, he could only say the soldier's partner was a lovely woman.
"With Willie I think it's a golden opportunity to build their relationship, make it stronger, but also have young people around them to move forward."
Mr Key added: "It helps at-risk kids in South Auckland and Willie's going to be a great role model for them. I'm sure he'll do a great job out there.
"It's a great loss, I think, to the SAS, but these guys are in a very high pressure environment. He's given a big part of his career to the army and obviously to the SAS, so we wish him all the very best."
Corporal Apiata is the only living New Zealander with a VC, the highest military honour.
He won the award for rescuing an injured fellow soldier under enemy fire in Afghanistan in 2004.
