Officers made the discovery when they stopped Kevin Sharrock as he drove a hired BMW on the M621 on December 9 last year.
Leeds Crown Court heard 34-year-old Sharrock told the officers: "I am glad you have stopped me. There is a lot of cash in the boot."
Sharrock, of Tong Drive, Farnley, Leeds, was initially arrested on suspicion of money laundering.
Robert Galley, prosecuting, said the officers then looked in the boot and found a large holdall.
He said: "The holdall didn't have a large quantity of money in it. It had a large quantity of cocaine in it."
The bag contained 15kg of the Class A drug in blocks which had a purity of up to 90 per cent.
Sharrock's fingerprints were not found on the blocks.
Mr Galley said it was the Crown's case that the defendant had been acting as a courier in a drug supply operation.
The cocaine was estimated to have a wholesale value of £525,000 and a street value of £1.5m.
Sharrock's home was searched and officers found high-value clothing items and a knuckle duster
The defendant refused to comment when interviewed.
He pleaded guilty to possessing a class A drug with intent to supply.
Sharrock has 16 previous convictions, including an offence of possessing amphetamines.
Adrian Pollard, mitigating, said Sharrock pleaded guilty at an early stage and accepted he would be facing a lengthy prison sentence.
Mr Pollard said the defendant became involved in the offence after getting into debt and had been delivering the drugs on behalf of others "higher up the food chain."
Recorder Andrew Latimer jailed Sharrock for eight years.
Speaking after the sentencing, Det Chief Inspector Andrew Howard of the Yorkshire and Humber Regional Organised Crime Unit said: “I welcome the sentence handed down by the court today, which reflects the serious organised criminality this individual was involved with. It should serve as a warning to others concerned in this kind of activity.
“I have no doubt that the drugs seized would have had a severe impact on our communities across the region.
“The Yorkshire and Humber Regional Organised Crime Unit continues to work to disrupt the organised production and supply of drugs across the region and tackle the associated criminality linked to these offences.”