Shahid Mohammed has been found guilty of murdering 8 members of the same family 17 years ago.
The Chisti family died when their home in Huddersfield was petrol-bombed in Birkby, Huddersfield, in 2002.
Those who died were Nafeesa Aziz, 35, and her daughters Tayyaba Bootall, three, Rabiah Bootall, 10, Ateeqa Nawaz, five, Aneesa Nawaz, two, and six-month-old Najeebah Nawaz.
Miss Aziz's brother, Ateeq, 18, also died in the fire, and their mother, Zaib-un-Nisa, 54, died a week later in hospital after jumping from a window to escape the flames.
The 37 year old had been investigated by police at the time but skipped bail and fled to Pakistan prior to a 2003 trial in which several other people were convicted for their involvement in the incident.
During a four-week trial at Leeds Crown Court, jurors heard that the blaze which caused the deaths of eight members of the Chisti family had followed a grudge that the defendant had been "pursuing vigorously".
Prosecutors said Mohammed, of no fixed address, reacted angrily when his sister, Shahida, became involved in a relationship with a man named Saud Pervez, of whom he did not approve.
One member of the Chisti family, Mohammed Ateeq-Ur-Rehman, known as Ateeq, had played an "active part" in the maintaining of their relationship, and was probably the target of the attack on May 12 2002, the court heard.
Relatives of those that died at the family home more than a decade ago gave their reaction to the conviction outside Leeds Crown Court.
West Yorkshire Police Detective Chief Superintendent Nick Wallen said: "All of us who have been on the investigation team are absolutely overjoyed at the guilty verdict.
West Yorkshire Fire and Rescue Service Area Manager, Chris Kirby, said: This was a tragic incident which had a devastating impact on the family and the wider community, as well as being distressing for the firefighters and investigators who dealt with the aftermath.
In this case the speed and ferocity of the fire gave little chance of escape due to accelerants being used.
We condemn deliberate fire setting in any circumstances however the details of this case are particularly abhorrent."
Mohammed will be sentenced on Wednesday.
Jon Hill reports on the events that unfolded after the fire that killed eight members of the same family.