Stuart Howarth, 32, of Oldham, near Manchester, pleaded guilty at Mold Crown Court to the manslaughter of David Howarth at his home in Penmaenmawr in Conwy.
He was jailed for two years.
After the case, he made a plea from his prison cell for people to listen to children when they claimed they were being abused, and to adults who later managed to talk about childhood attacks.
Howarth's guilty plea was entered on the basis of diminished responsibility and he claimed he attacked his 55-year-old stepfather with a hammer after suffering flashbacks to his childhood.
The jury was told that Howarth suffered horrific sexual, physical and emotional abuse at the hands of his stepfather, beginning when he was just five or six years old.
Howarth had not seen his stepfather for10 years, but discovered where he lived on a visit to north Wales.
Asked for help
He later returned to the victim's terraced home and hit him over the head with a 3lb lump hammer, before driving back to Manchester and giving himself up to police.
The court was told the victim had been jailed for four years for sexually abusing his stepdaughters, one of whom was confined to a wheelchair and had since died.
In a statement written in his prison cell after sentence, Howarth said he had continually asked for help.
"I never wanted this to happen," he said.
"When I was five-years-old, adoption magistrates asked me if I liked my new father, David Howarth.
"I said yes but not when he hurt me. They laughed and ignored what I said. That was how my life continued for the next 28 years.
"No one wanted to listen to me, no one wanted to help me.
Confronted
"We must listen to children when they tell us that they are being hurt. We must also begin to listen to men and women who were abused as children when they ask for help as I did so many times."
Howarth said that finally, in desperation, he turned to his stepfather for help. He confronted him and tried to understand him, but the meeting went tragically wrong.
He denied that he had gone to his stepfather's home to get revenge.
"I am not now, nor have I ever been in favour of vigilantism," he said.
'Appalling and depraved'
" I am not happy about his death and there is nothing to celebrate."
Mr Justice Elias told him that there was overwhelming evidence in Howarth's statements that he had regularly been subjected to the most appalling and depraved acts of sexual, physical and emotional abuse from the age of five.
"They reflect acts of the utmost depravity," he said, and added that it was clear that his childhood experiences had left him scarred.
Psychiatric reports on Howarth showed that at the time of the attack he was suffering from a borderline personality disorder and probably also post-traumatic stress disorder, too.
Childhood memories
It was clear his condition had substantially impaired him responsibility for his actions.
The day he found his stepfather's address and went to confront him, his childhood memories were revived by certain features of the house which reminded him of his old home.
Sentencing Howarth, the judge concluded that he was not considered a serious risk to others, but he had to impose a jail sentence because of the gravity of the offence.
"The law must protect life whatever the character defects of the deceased," Mr Elias said.