The 33-year-old told a jury she was regularly molested in her family home from the age of six until she was 15 or 16 by Michael Burke, who is five years older than her.
She said: “Most people remember their first time having sex with somebody they love. Whereas my first time of having sex was with my brother.
“It’s horrible. Even now I can’t sleep naked. I can’t even cuddle in bed.
“I will never love properly, I will never be able to let someone in. It’s horrible.”
Burke, 38, described as a “controlling and violent” man, denied 15 counts of rape, one attempted rape and one indecent assault against his sister and two other women over an 18-year period between 1992 and 2010.
The jury found him guilty of eight counts of rape and another serious sexual offence against three women – including three counts of rape against his sister between 1992 and 1994.
He was cleared of nine other serious sexual offences.
Karen Danczuk initially revealed she had been abused – without naming her attacker – in an interview with The Sun in February last year.
Two other victims came forward after she went public. They cannot be named for legal reasons.
During the trial, Mrs Danczuk gave evidence from behind a curtain.
The mother-of-two said she was a “quiet” child who was “heavily bullied” growing up in Middleton, near Rochdale.
She told the court the abuse started as a “game of hide and seek” when she was six or seven, where her brother would lie next to her in bed.
From there the abuse progressed to rape on a weekly basis when she was 11 and lasting until she was 16.
Mrs Danczuk told the court it had “ruined” her schooling, with her leaving education with “crap” qualifications.
She said: “My anxiety, I have suffered with depression and anxiety through the majority of my adult life.
“I can’t love anyone. It sounds terrible. I’m just waiting every single time for someone to hurt me. It’s just been horrible.”
During cross-examination, defence lawyer Nigel Power QC questioned why she went to the papers before the police and accused her of “attention seeking”.
Mrs Danczuk replied: “This idea that it is just attention, this has ruined my life. I have had a horrendous life, it’s a fact.”
She added that sometimes “being dead makes more sense than being alive”.
Burke will be sentenced on 15 December