The 71-year-old man, who cannot be identified to protect his victims, assaulted his three biological children and a stepdaughter over more than two decades.

He has pleaded guilty to more than on 30 counts of rape, indecent treatment and assault in the Brisbane District Court on Tuesday.

The assaults started when the girls were as young as six with sexualised touching before progressing to rape and oral sex.

The brazen assaults often metres from other family members had a "profound and lifelong" effect on his victims, the court was told.

One daughter bravely stared down her father as she gave a powerful victim impact statement.

"A child's innocence is such a precious gift, and no one has the right to destroy that innocence," she said.

"I am fearless - not because of bravery but because years of having the monster come into your bedroom at night or into your private space in the day conditions you to not feel anything."

She told the court she lived a "half-life" and was unable to maintain meaningful relationships with other people.

"This is because my father, someone supposed to protect you, sexually abused me for the first 14 years of my life.

"There is also psychological abuse - being told variously by my father that 'I am helping you to be a better wife in the future and not be frigid and this is a special thing between me and you ... completely distorts reality."

The father's defence team said he had been sexually abused as a child and had been physically assaulted while in custody.

His sentence will be handed down on Thursday.

Australian Associated Press