David Redfern, 46, dragged Margaret Barnes out of bed and down the stairs in his seaside home in Barmouth before kicking her on the floor.
Mrs Barnes, a retired factory worker from Birmingham, died of severe internal injuries.
Redfern, 46, was given a life sentence at Caernarfon Crown Court on Friday.
Mr Justice Bourne said that the 14 years, less the time he had served on remand in custody, was the minimum time he would spent in prison before a parole board decided whether he was fit for release.
Margaret Barnes' daughter, Natalie Barnes, told the court the murder had "completely destroyed our family life".
Speaking after the sentence Detective Superintendent Mark Pierce said: “We welcome today’s life sentence for David Redfern for the brutal murder of Margaret Barnes.
"During a two-week trial Redfern showed no remorse, attempted to blame Margaret for his actions and subjected her family to the trauma of a two-week trial where details of the event were explored in graphic detail. How a 21 stone, 6ft1ins man could have inflicted such catastrophic injuries on a frail, 71-year-old lady, 25 years his senior, is beyond the comprehension of any reasonable person.
“David Redfern is a cowardly, vicious bully and will now spend at least 14 years behind bars where he can reflect on what he has done.”
A 46-year-old man has today been sentenced to life in prison for murder.— North Wales Police (@NWPolice) March 31, 2023
David Redfern, of Marine Parade, Barmouth, denied killing 71-year-old Margaret Barnes on July 11th 2022, but was found guilty by a jury on March 29th.
➡️ https://t.co/1B4jU1wx8H pic.twitter.com/GenkDWA55T
The bank IT worker, of Barmouth, Gwynedd, had refused to call an ambulance as Mrs Barnes lay dying outside his five-storey townhouse last July.
He had denied murder or manslaughter but was convicted of murder by a jury after 14 hours and 30 minutes of deliberations.
During the trial Michael Jones KC said Redfern, a 21-stone, 6ft, angry bully had dragged Mrs Barnes, a retired factory worker from Birmingham, downstairs by her ankles after finding her in his bed.
Redfern claimed Mrs Barnes became “agitated” when he made a 999 call to police. He said he went into his bedroom with his fiancee to find Mrs Barnes in the bed and said he just wanted to get her out.
He told the jury he fell on top of Mrs Barnes. But a camera recorded him saying he was sorry for kicking her and dragging her downstairs.
After the verdict, Mrs Barnes’s family said: “Margaret, who was a much-loved wife, mother and grandmother, has now been gone for eight months. As a family it has been the hardest time of our lives.
"It has been especially difficult for Margaret’s husband, who had been her partner for 56 years. We now have some sort of closure on what has happened, however, no length of sentence will ever fill the void that Margaret has left behind.”
“As a family we would like to thank the police for their hard work in putting the case together.”