Homeless Deyan Deyanov, 29, was convicted by a jury of nine at the Provincial Court in Santa Cruz de Tenerife for the frenzied knife attack on the holiday island two years ago.
He repeatedly stabbed then beheaded Jennifer Mills-Westley, 60, originally from Norwich, who had been shopping in the popular resort of Los Cristianos on May 13, 2011.
Onlookers watched in horror as the deranged killer then walked out of the store carrying his victim's head, before being wrestled to the ground and arrested.
His defence had argued he was not criminally responsible for his actions because he suffers acute paranoid schizophrenia, but he now faces a sentence of 15 to 20 years in a psychiatric unit after being found guilty of the crime under Spanish law.
The devastated family criticised the legal process and governmental support following the ordeal of the trial.
The victim's youngest daughter Samantha Mills-Westley, 39, who lives in France, was joined in court by her sister Sarah Mills-Westley, 43, from Norwich, and her partner Brian Moore, 41, the victim's brother John Smith, 63, and his wife Julie Smith, 62.
In a statement, they said: "Since May 13 2011, Jennifer Mills-Westley has become known as the lady who was beheaded in Tenerife. The truth is she was our mum, our mentor and our best friend.
"She was a highly gifted, selfless person with so much love in her heart and who has been taken away from us in her prime.
"It's hard to put into words the devastating impact that this preventable and needless act has had on us as a family; sadly mum was in the wrong place at the wrong time."
A warrant for the killer's arrest had been issued just three days before he murdered Ms Mills-Westley, but officers were unable to locate him.
At 10.30am on the day of the crime he went into the shop, picked up a nine-inch-long knife and plunged it repeatedly into Ms Mills-Westley's neck.
The crack cocaine and LSD user was well-known to police on the island and had been arrested at least four times since January 2011 for violent offences.
At one stage Interpol said they planned to investigate his movements during a spell when he lived in the Scottish capital.
He was working as a labourer in Edinburgh as recently as 2010 and his former flatmate, Vlad Chmurny, said the killer was a fantasist who spent most of the day taking drugs in a tenement in Halmyre Street, Leith.
Wearing an olive green hooded top, black tracksuit trousers and running shoes, Deyanov remained quiet and still as the verdict was read out yesterday.
Asked by magistrate Maria Jesus Garcia Sanchez if he had anything he wanted to say, he told his Bulgarian interpreter: "I am the second reincarnation of Jesus Christ and I will bring the fire of the Holy Spirit to bear against this court."