Charlize Theron's dad fired off three shots first before he was shot dead by her mother.
Opening up about the 1991 incident on a National Public Radio broadcast, the actress, 44, said: "My father was so drunk he shouldn't have been able to walk when he came into the house with a gun.
"My mum and I were in my bedroom leaning against the door because he was trying to push through the door.
"He took a step back and just shot through the door three times."
Theron, who was 15 then, said it was a "miracle" they were not killed. Her mother had no choice but to act "in self-defence" and "ended the threat".
Theron's parents were co-owners of a road construction company.
The shooting incident has since prompted the Oscar winner to support efforts to combat family violence.
Describing her father as a "very sick man" and noting that he was an "alcoholic all my life", Theron said: "I'm not ashamed to talk about it because I do think the more we talk about these things, the more we realise we are not alone in any of it.
"I think, for me, it's just always been that this story is about growing up with addicts and what that does to a person."
Her latest movie, Bombshell, deals with another toxic topic - sexual harassment at Fox News.