Roy Webster has been given a mandatory life sentence for the murder of Anne Shortall in Wicklow two years ago.
She had threatened to tell his wife about their one night stand.
The jury earlier returned a unanimous verdict in the case.
Webster, 40, from Ashbree, Ashford, Co Wicklow, had pleaded guilty to the manslaughter of Ms Shortall in April 2015, but had claimed he did not intend to kill her and pleaded not guilty to murder.
The court heard Ms Shortall, 47, claimed to be pregnant and Mr Webster said she had asked him for £6,500 Sterling for an abortion.
He told gardaí he met her on 3 April 2015 to get proof of her pregnancy and then intended to get money for her.
But the court heard she did not bring any proof. He said he hit her on the head with a hammer after she stormed out of his van and then hit her again after she said she would ruin him.
The court heard she had been hit nine times on the head with a hammer. The jurors were also told Ms Shortall was not pregnant and knew that.
Webster wrapped Ms Shortall's head and hands with duct tape. The State Pathologist said she could not determine if Ms Shortall was dead or alive when the tape was wrapped around her head.
Afterwards, Webster drove home and was "acting completely normally" according to evidence heard in court. He had a glass of wine, watched television and went to sleep on the couch the court heard.
He moved Ms Shortall's body to his work shed the following day after opening his van to get some wood.
The following day he told gardaí he had a "pyjama day" and watched a film.
He finally confessed to killing Ms Shortall four days later, after gardaí called to his home and his wife asked him if he had hurt Ms Shortall.
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He told gardaí it was like having an out-of-body experience or watching a horror movie as he hit her on the head.
He said it was as though he had snapped because she had him backed against a wall and was going to ruin him and his family.
His lawyers had told the court he lost control and that the jury should consider the defence of provocation.
Lawyers for the Director of Public Prosecutions said Webster's statements to gardaí after his confession had a degree of "self pity".
They also said despite the evidence that had been heard about Ms Shortall and her background, it was Roy Webster who was on trial.
What the jury had to decide was whether or not he had intended to kill her.
After more than seven and a half hours of deliberations since Tuesday, the jury found him guilty of murder by unanimous verdict.
Mr Justice Patrick McCarthy sentenced Webster to life in prison this afternoon.
Court hears victim impact statements
Before Webster was sentenced to life in prison, victim impact statements were read to the court on behalf of each of Anne Shorthall's children - Alanna, Emma and David.
In a written statement read to the court by Alanna, David said: "On Wednesday I should have been embracing my mother with open arms and saying "happy birthday". Instead I put flowers on her grave."
Emma said she had lost her mam, best friend and confidante. She added: "There is a void in my life that can never be filled."
Alanna said the person she relied on most was taken away "suddenly and violently.
"My mother was not meant to die, her life was taken from her. She will never get to see her grandchildren grow up," she said.
Anne's siblings and close family penned a joint statement revealing Anne's brother James became so depressed by what had happened that he took his own life seven weeks after her brutal murder.
"Our family will never be the same," they said.
Webster's barrister Brendan Grehan SC then stood up to tell the court that his client wanted to say sorry to all who had been affected, especially the children of Anne Shortall and his own family.
He added that while he "bitterly regrets" what happened, "it was never his intention to injure her, much less kill her."
Webster, who shook his head in disbelief when the verdict was revealed earlier in the day, wept before the judge asked him to stand while he passed sentence.
Justice McCarthy said: "As a matter of law there is one penalty only and I imprison you to life." As prison officers brought him from court one final time he mouthed "sorry" in the direction of Ms Shortall's family.
His sentence was backdated to 7 April 2015, when he first went into custody.
