The 78-year-old New Zealand actor, who lives in Central Otago, was diagnosed with stage three blood cancer four years ago.
"I've been living with a particular type of lymphoma. I was on chemotherapy and the pretty miserable business but it was keeping me alive," Neill told 7News.
"Then the chemo stopped working. I was at a loss and it looked like I was on the way out, which wasn't ideal, obviously."
Sir Sam ultimately underwent CAR T-cell therapy to train his immune cells to recognise and destroy cancer, and the results have been remarkable.
The actor - whose film credits include The Hunt For Red October, The Piano, The Dish and Jurassic Park - said: "I've just had a scan just now and there is no cancer in my body.
"That's an extraordinary thing. I'm very, very excited that this can happen."
He first revealed news of his cancer battle in his book Did I Ever Tell You This?, which he started work on following his diagnosis.
"I'm not afraid to die, but it would annoy me," he said at the time.
"Because I'd really like another decade or two, you know? We've built all these lovely terraces, we've got these olive trees and cypresses.
"I want to be around to see it all mature. And I've got my lovely little grandchildren. I want to see them get big. But as for the dying? I couldn't care less."
An outspoken critic of the proposed Santana Minerals open-cast gold mine near his vineyard, Sir Sam recently revealed he had been subjected to threats of violence and personal attacks.
He said stood by his views on the mine and was glad he voiced them.
"What I wasn’t prepared for was the personal abuse I would come in for."
