The rare nitrate film dates from 1912 and shows goldminers in Lawrence and scenes of early Dunedin.
It was found among family memorabilia and donated to the New Zealand Film Archive by Kirk Robertson.
"It's something that's just been passed down from generation to generation," Mr Robertson said on Wednesday.
"I was quite surprised at how excited they were about it. I didn't see the significance of it."
Mr Robertson's great-great-great-grandfather, Peter Robertson, was the second settler in Lawrence and his great-great-grandfather, James Robertson, was mayor of the township from 1907 to 1916.
"Gabriel Read used to stay in Peter Robinson's cottage. When my great-great-grandfather James was 13 or 14, he used to go prospecting with Gabriel Read. He later became the mayor of Lawrence and organised the Gabriel's Gully jubilee in 1911.
"It was amazing to see the film. How many people get to see their great-great grandfather in the flesh?"
Mr Robertson will be displaying his family memorabilia at the "Layers of Gold" Otago Heritage Festival in Lawrence at Gabriel's Gully during Otago Anniversary weekend, from March 18 to 21.
"This film is incredibly exciting," New Zealand Film Archive national programmes manager Jane Paul said.
"It's also unusual, because he knows the people in it and where it came from, as it's been passed through generations of his family.
"We're absolutely rapt to have it. This film is so early; it was made almost 100 years ago. We've got nothing on those goldminers from that era, so it's incredibly important in that way," she said.
"It's also incredibly encouraging that this nitrate film was discovered in Dunedin. It makes you wonder what else people have squirrelled away.
"Nitrate wasn't being used by the 1950s and a lot of it was just thrown out at the tip, because it's highly-flammable and people were worried about it burning their houses down."
The film would be digitised and hopefully premiered at the Otago Heritage Festival, Ms Paul said.
The Film Archive was scheduled to screen a compilation of 15 short films shot in Otago and Southland between 1911 and 1940 in the Dunedin Public Art Gallery at 4pm and 7.30pm, yesterday.
The films include scenes of the 1912 Highland Games in Dunedin, the University of Otago Carnival Day in 1926, the Duke of York visiting Dunedin in 1927, a monkey and peanut vendor in 1933, the St John Ambulance baby contest in 1940 and films by New Zealand cinematic pioneer Len Lye.
The screenings also featured a live piano accompaniment by Eli Gray-Smith.
