Afshan Azad, 21, who played Padma Patil, a classmate of the teenage wizard, in the blockbuster Hollywood films based on JK Rowling's children's books, feared for her life during the three-hour ordeal, Manchester Crown Court heard.
She was punched, dragged around by her hair and strangled by her brother Ashraf Azad, 28, who threatened to kill her after he caught her talking on the phone to her Hindu boyfriend on May 21 last year, the court was told.
During the row at the family home in Longsight, Manchester, which also involved her mother and father, she was branded a "slag" and a "prostitute" and told: "Marry a Muslim or you die!"
The actress, who now lives in London, had pleaded for leniency from the court, begging the judge not to jail her older brother.
But Judge Roger Thomas QC sent him to prison for six months after he pleaded guilty to the assault.
"This persistent attack was accompanied by serious and very hurtful abuse and threats," he told the defendant.
"It must have been a miserable and frightening experience for your sister which, she suggested, lasted for about three hours or so.
"The background to this offence lies in the concern that you, and perhaps other family members, had about Afshan's relationship with a young man who was not of the Islamic faith."
Judge Thomas added: "This is a sentence that is designed to punish you for what you did and also to send out a clear message to others that domestic violence involving circumstances such as have arisen here cannot be tolerated."
Earlier, the court heard that the actress's family are devout Muslims but she had begun a "romantic relationship" with a Hindu man.
Richard Vardon QC, prosecuting, said: "Apparently that was a cause of some concern as far as Afshan was concerned. She realised her family would never accept the relationship."
At about 7pm on May 21 last year, she was in her bedroom at the family home, talking on her mobile - and was overheard by her brother in the bathroom, who assumed it was her Hindu boyfriend.
"I can hear you from here," he shouted, before adding: "Who the f*** do you think you are talking to? Watch what I will do."
Mr Vardon said Miss Azad ended the call, hid the phone and sim card and then sat on her bed before the defendant barged in and began shouting at her.
"He then grabbed her hair and threw her across the room," the prosecutor said.
"He pulled her by the hair and threw her on the floor.
"She began crying and asked him to stop. The defendant began punching her with clenched fists to her back and head area."
As the actress cowered in a ball on the floor, her brother's wife, Sonia, who also lived at the address, came into the room and tried to push him away.
"He told her to stay out of it," Mr Vardon continued, "because he would do what he wanted with his little sister.
"He grabbed her by the hair and pulled her up from the floor, dragging her downstairs to her father's bedroom."
She was pushed on to her father's bed, with her brother shouting: "Sort your daughter out! She's a slag!"
Her father may then have said: "Just kill her!" - although this was disputed in court because of his Punjabi accent.
The defendant then grabbed her by the neck and began to throttle her, the court heard.
"She struggled to breathe and was scared for her life," Mr Vardon added.
The victim's mother and sister-in-law then entered the bedroom as the family discussed what to do with her, the court was told.
Her father, Abul, 53, suggested sending her back to Bangladesh for an arranged marriage.
Her mother called her a "prostitute" and asked her how many men she had been with, adding: "Why are you obsessed with sex?"
The defendant then said: "I'm going to kill you. I'm actually going to kill you", and left the room, with the door locked behind him by one of the women.
He was then heard "rattling through kitchen drawers" before shouting: "Where are the knives?" - thought to have been hidden by his wife.
"She was told she had to marry a Muslim or you die," Mr Vardon added, and her parents began asking who she wanted to marry and making a list.
The defendant then said he had found in her bedroom a passport photo of the Hindu boyfriend and went to look for him.
By 10pm calm was restored and Miss Azad's father sent her to bed, but she fled the family home the next day through her bedroom window.
"She realised she would have to leave and felt she could not live any longer in that environment," Mr Vardon said.
"She was genuinely fearing for her life."
The assault left Miss Azad with swelling, grazes and bruises around her eyes, face, left ear, forehead and forearms.
Both her father and brother were originally charged with making threats to kill her and her brother was also charged with assault.
Instead of both going on trial, at a hearing last month the prosecution agreed to accept a plea of guilty to assault from her brother, and both men were formally found not guilty of making threats to kill.
Her father accepted being bound over to keep the peace for 12 months in the sum of £500.
During the last hearing, lawyers said attempts to get the victim to come to court to give evidence against her father and brother had been unsuccessful and Miss Azad would not attend voluntarily.
The court heard that the actress, who now lives in London, had written a letter to the judge asking for "leniency" to allow her to "return to the family".
"She expresses forgiveness towards her brother," the judge said, reading from the letter.
"She expresses good feelings about her family in general and brother in particular. She doesn't wish to support the prosecution. She expresses concern about being estranged from her family."
Peter Clarke, mitigating, said the family were "extremely proud" of her film career and blamed the defendant's drinking before the attack for the incident.
"He is utterly ashamed by his behaviour," he said.
"He's at a loss to explain his behaviour. He had been drinking."
In the Harry Potter films Miss Azad played a witch who was in the same year as the teenage wizard, played by Daniel Radcliffe, at Hogwarts School Of Witchcraft And Wizardry.
She first appeared as her character, the identical twin sister of Parvati Patil, in Harry Potter And The Goblet Of Fire and also starred in Harry Potter And The Deathly Hallows, the final film in the saga.
