Seven years ago, he decided to "stop waiting for the phone to ring" and start his own film and television company, Awa Films. The awa in question is the Whanganui River. He now lives in Wellington but returns to Raetihi often.
The other siblings in the family lead more normal lives. One is an electrical engineer, another works in early childhood.
"They're all sane. It's only me and my brother who are crazy and want to torture ourselves," he said.
Growing up in small-town New Zealand in the 1970s and 80s was great. Young Julian delivered the Wanganui Chronicle and played a lot of sport.
Raetihi was pumping with agriculture and forestry, and a timber mill. All the shops were full, and trips were made to Wanganui for major shopping.
When Julian was 11, his film producer father came into his life. It was 1983, and Larry Parr was about to direct his first short film, The Makutu on Mrs Jones. He shot it at Whangamomona and Julian had a part.
"It all came as something new to me. I wasn't even in the drama club and I didn't even like doing the stage plays at school."
Film types were different from the farmers, timber workers and shopkeepers of his small town.
"The film industry opened my eyes to a whole different group of people, people who made a living from creativity."
Leaving home in his mid-teens, he moved to Auckland, hassled his father's film friends for jobs and did a 12-year apprenticeship in the industry as a technician. One of the people he came across was Lee Tamahori, the director of Once Were Warriors.
Aged 22, Mr Arahanga auditioned for the part of Nig Heke, the son of the terrifying Jake the Muss, and he got it. Working on that film was special, he said.
The film showed rape, suicide, violence, alcoholism and despair in an urban Maori setting - and the actors had no idea how the public would react.
"We were thinking, 'Oh man, how are people going to respond to this film'. The critics and doubters were not just Pakeha. Maori were saying 'Why are you making this film? You guys are going to give us a bad name"."
When Once Were Warriors came out, it was so good that criticism died away.
"The whole thing is a really, really well executed film. It's just so intense the whole way. It doesn't really let you rest."
After it, Mr Arahanga returned to his film technician work, and in 1996 he went to New York. He was out one day when he got a call from Sydney, saying the Wachowski brothers wanted to see him for a part in The Matrix. He had never heard of The Matrix or the brothers.
He went home, had a shower and was picked up in a limousine two hours later and flown to Los Angeles. He read the film script in a hotel. The next day, the brothers - " two rough, rough looking dudes" - came to talk to him and he got the part.
He's since had other roles, including in Broken English, Fracture and What Becomes of the Broken Hearted?
But for the past seven years, he's been directing and producing. Awa Films made Turangarere, a documentary about Maori bomber pilot John Pohe, and television series Songs from the Inside, putting prisoners' lives into songs.
It's now working on Behind the Brush, about painter Gottfried Lindauer, and has two years' worth of work ahead of it.
His focus has changed to directing, but Mr Arahanga isn't ruling out more acting roles.
"I would never say never for acting. My door is always open for that kind of thing."
