Romanian national Cristian Sabou will serve a minimum of 23 years behind bars after he was found guilty of killing Mrs Graves at a home in Bosham, West Sussex.
Ms Greaves had been house sitting at a £1.6million property in the small village of Bosham, West Sussex, when she was killed in a burglary gone wrong.
The artist was found dead on the ground floor bedroom of the property having suffered serious head injuries.
Sabou pleaded guilty to her murder when he appeared at Lewes Crown Court on Monday.
Prosecutor Philip Bennetts QC said: “There were extensive injuries to her head.
“The level of force used was extreme. Not dissimilar from the forces experienced during road traffic collisions.”
The court heard the 28-year-old had expected the home to be empty, having worked odd jobs for the homeowners in previous months.
He had previously been informed that a safe in the house contained a large amount of cash and gold ingots.
However when he found Ms Graves inside, he struck her with a hammer.
“Rather than simply running away in the hope you could not be identified by a woman waking from sleep you conducted this horrific attack on Ms Graves,” Judge Christine Laing QC said.
“It was your dishonesty and greed that took you to the house. It was your cowardice and lack of morality that caused you to kill Valerie Graves.”
Ms Graves, who had lived in Scotland for almost 10 years before her death, was described as a “free spirit” who was “always hungry for a new challenge” by her family.
They said in a statement: “This has been a devastating experience for the whole family and today we feel that justice has finally been served.
“We have had to endure six years of waiting, not knowing if anyone would ever be brought to justice for this cowardly act.”
They added: “You took away our mum, who was also a sister, daughter, gran and friend to many – a life of someone who can never be replaced.
“We hope that, while he is serving his sentence, he will reflect on the actions he took and what this has done to our family.”