Entwistle was convicted of shooting his 27-year-old wife Rachel and their nine-month-old daughter Lillian Rose at their new home in Hopkinton, Massachusetts, on January 20, 2006.
The 29-year-old former computer worker, from Kilton, Worksop, was found guilty of first degree murder after around 13 hours of jury deliberations at the Middlesex County Superior Court in Woburn, Massachusetts.
Entwistle was convicted of first degree murder and will be sentenced to life in prison without the possibility of parole.
The judge adjourned sentencing until tomorrow and remanded Entwistle back into custody.
Entwistle, wearing a black suit with a blue tie, looked down as the jury returned its verdicts before closing his eyes.
As he sat down in his seat after the verdicts were returned, his defence lawyer, Stephanie Page, patted him gently on the shoulder.
His parents, Yvonne and Clifford, and his younger brother Russell, all from Kilton, Worksop, did not react as the verdicts were returned and looked straight ahead as the judge dismissed the jury.
Entwistle was also found guilty of unlawful possession of a firearm and ammunition.
He had a secret life in which he trawled the internet for escorts and looked at websites about sex, killing and suicide before shooting dead his wife and baby daughter.
In the days before the murders, he trawled sex websites, including the sex and swinger community Adult Friend Finder, looking for "a bit more fun in the bedroom" and searched the internet for "how to kill with a knife".
US prosecutors have said they investigated the possibility of a murder-suicide, with Entwistle failing to kill himself.
His parents, school dinnerlady Yvonne and Bassetlaw district councillor Clifford, were in court every day, with their younger son Russell by their side, as US prosecutors exposed the darker side of their oldest son's life.
They always said Entwistle was "100% innocent", but across the aisle on the front row of the public gallery, Mrs Entwistle's mother Priscilla and stepfather Joseph Matterazzo accused him of an "unbearable" betrayal.
The Matterazzos showed little outward emotion as they sat through each day of the "sordid, gruesome and graphic" evidence.
Entwistle was jobless, his eBay scams and internet businesses were failing, and he had no means of support when he joined his wife and daughter in the US in September 2005, a month after they had crossed the Atlantic to live with the Matterazzos.
Along with mounting debts at the time of the murders, he had also just paid more than £4,000 upfront for a three-month lease on the four-bedroom colonial-style house in Hopkinton, which the young family moved into less than 10 days earlier.
Furniture for their new home, thousands of miles away from Entwistle's friends and family in Nottinghamshire, was being put on his seven credit cards and the couple, who met at the University of York where Rachel studied during her year abroad, had to ask her family for help to rent the BMW X3.
Entwistle used his father-in-law's .22 calibre Colt revolver, which Mr Matterazzo and his sons used for sports shooting, to kill his wife and baby on January 20, 2006, the day before Mrs Entwistle's mother Priscilla and friend Joanna Gately were due to visit.
The jury was shown detailed photographs and a harrowing 20-minute video of the bodies, which lay undiscovered for two days, hidden under a bloody blanket, duvet and pillows on the middle of the four-poster bed.
It was a rare moment of emotion for Entwistle, who broke down in court and was comforted by his legal team.
The blood-stained pyjamas, T-shirt and underwear worn by his young wife and daughter when they were killed were also held up in court.
The day after the killings, he fled to England on a one-way ticket, collecting as much money as he could from several cash machines in New England, and dumping his car, which contained keys to his in-laws' home in Carver, Massachusetts - where the gun was found - at Boston's Logan International Airport.
But he did not arrive at his parents' Worksop home until at least 36 hours after landing in London, instead travelling about 800 miles around the UK and staying at a hotel just one hour's drive from his parents' home.
Later, he spent time with his friends from the University of York's rowing club, Dashiel Munding and Benjamin Pryor, eating out in London and visiting the cinema, before his arrest at the Royal Oak Underground station on February 9, 2006.
On that day, he was carrying a note which the court heard showed the "two sides of Neil Entwistle".
On one side he wrote how much he loved his wife and daughter, while on the other were details of how he planned to sell his story to the highest bidder.
In January last year, while on remand in Cambridge, Massachusetts, he was sent to a psychiatric hospital after US prison guards found a letter to his parents reportedly saying it could be his last, and giving instructions for his burial.
During the trial, a total of 46 prosecution witnesses gave evidence against him but US prosecutors were never given the chance to cross-examine the defendant.
But Entwistle denied he was responsible for the deaths during a recorded phone call with state trooper Robert Manning, in which he said he realised that fleeing to England "did not look good" and confessed he had not cried "properly" since the killings.
For the defence, Elliot Weinstein offered no witnesses of his own but suggested Mrs Entwistle killed baby Lillian before committing suicide and that Entwistle was simply a loving husband trying to "protect her honour" and cover it up by moving the gun away from where their bodies were found.
But the jury did not believe the cowboy boot-wearing lawyer.
Mrs Entwistle and Russell did not stand up as the jury entered the courtroom, but Mr Entwistle did.
As Entwistle was taken down, he shrugged his shoulders at his parents.
Outside court, Mrs Entwistle said: "We know that our son Neil is innocent and we are devastated to learn that the evidence points to Rachel murdering our grandchild and then committing suicide.
"I knew Rachel was depressed. Our son will now go to jail for loving, honouring and protecting his wife's memory."
Mr Entwistle added: "From the moment the Matterazzo spokesman Joe Flaherty stated, and I quote, 'All we need now is the right jury pool', we knew Neil would not receive a fair trial.
"We will continue to fight for our innocent son with the hope that one day justice will prevail and our little granddaughter Lilly may rest in peace."
Entwistle's lawyer Elliot Weinstein said it had been a "very sad case" for the two families and confirmed he would appeal.
He said that he was "confident" the case would meet a successful review in the Supreme Court.
"We believe that under a different environment people selected to hear this evidence would have reached a different result," he said.
Earlier in court, Rachel's parents shook hands with the US prosecutors as they left the court after the jury was dismissed.
Moments before the verdict, Ms Page had straightened Entwistle's tie for him as he took his seat next to his lawyers.
He nodded as he chatted with his defence team while waiting for the jury to enter.
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