Malcolm Webster, 54, was jailed for a minimum of 30 years for killing Claire Morris, 32, in the planned smash in Aberdeenshire in 1994 and attempting to kill Felicity Drumm in New Zealand in 1999 to claim insurance money.
The former nurse, from Guildford, Surrey, was handed the life sentence after being convicted of the crimes in May 2011 following a five-month trial.
Judges at the Court of Appeal in Edinburgh today rejected a claim that he was the victim of a miscarriage of justice.
Webster's legal team argued that scientific experts who gave evidence at the trial had not been able to rule out the possibility that the fatal car fire started accidentally.
As a result there was insufficient evidence for the jury to conclude that Ms Morris had been murdered, they said.
But Lord Eassie, delivering the opinion of the three appeal judges, said: "While, as scientists, the expert witnesses in question could understandably not exclude in scientific terms the ultimate possibility of an accidental ignition, there was nothing in their testimony offering any real, positive support for a contention that, given the interval before it erupted, this fire was accidental."
The judge added that the prosecution case that the fire was started deliberately did not rely solely on expert evidence.
"In our view, the trial judge was correct to conclude that the evidence of the various, wider circumstances to which we have referred constituted a sufficient case to answer," he said.
Lawyers for Webster attacked the decision of trial judge Lord Bannatyne to allow the Crown to call a late witness, farm worker Ian Hardie, who contacted prosecutors only after the trial had begun.
Mr Hardie gave evidence that he had seen Webster at the site of the fatal crash 11 days before it occurred. Prosecutors argued that this was him familiarising himself with the spot before staging the crash.
Webster's lawyers said extensive media coverage of the trial had created prejudice which called Mr Hardie's identification into question.
But Lord Eassie said: "Put shortly, Mr Hardie's emergence as a potentially material witness came to all engaged in the trial as something wholly unexpected.
"It was, of course, handled wholly responsibly by all involved.
"The assessment of prejudice was a matter of assessment for the trial judge when he came to consider whether he should exercise his discretion to allow the additional evidence to be led. We have come to the view that his assessment is not open to successful challenge."
Webster's legal team also argued that the significant differences between the murder of Ms Morris and the attempted murder of Ms Drumm meant the two crimes did not corroborate each other.
This argument was dismissed by the appeal judges as "not well-founded".
Two of Webster's lesser convictions for fireraising were quashed.
Lord Eassie said: "For the rest, the appeal against conviction fails and must be refused."
A hearing on Webster's appeal against sentence will be held at a later date.
Sentencing him in July 2011, Lord Bannatyne condemned his ''cold-blooded, brutal and callous'' crimes, driven by an insatiable appetite for money and which formed part of a fraudulent plot to pocket almost £1 million in insurance payouts.
The trial spanned five months, making it the longest murder trial against a single accused in Scottish legal history.
Webster claimed the death of Ms Morris was a tragic accident which happened when he swerved to avoid a motorcyclist.
The jury heard the killer drugged her before driving the car they were in off an Aberdeenshire road and starting a fire while she lay unconscious inside.
He fraudulently claimed more than £200,000 from insurance policies following her death, later spending it on a Range Rover car, a yacht and on seducing a string of women.
In 1999 he tried to murder Ms Drumm in a copycat car crash in New Zealand in an attempt to claim more than £750,000 of insurance money.
Police started investigating Webster's past when one of Ms Drumm's sisters contacted British police in June 2006 to report her suspicions about him.
After the investigation into Ms Morris's death was reopened in 2008, forensic tests on a tissue sample from her liver revealed she had been given a sedative before the crash.