A driver dragged his French bulldog for 13 miles without realising his pet's lead was caught in the trailer.
James Price had not checked before setting off from his home in St Helens, Merseyside, to drive to work.
The following morning a member of the public discovered Pepper the dog's mangled body lying in the street.
Price pleaded guilty to causing unnecessary suffering to a protected animal at Sefton Magistrates' Court.
He admitted he "ought to have known the animal was not entangled in a vehicle".
Initially RSPCA inspectors referred to the incident as a "barbaric act of cruelty" but the court heard 36-year-old Price had "never intended" to harm the dog.
Pepper belonged to Price's young daughte, and had been in a kennel at the back of the driveway, the Liverpool Echo reports.
Price, who drives a low-loader for a living, had set off for work at around 5am and did not realise the dog's lead had become entangled in the trailer.
CCTV footage obtained by the RSPCA showed the lead snapping, but still Price did not realise what had happened and carried on his journey.
Inspectors eventually tracked him down via the microchip in the dog's body.
Daniel Kenyon, representing Price, told the court the loss of a family pet had been "punishment enough".
Price was banned from keeping animals for 12 months and ordered to pay £1,238 in fines and costs.
Magistrate Frank Dainty, passing sentence said: "I do not believe you intended to harm the animal, but in future you need to check every corner of your vehicle before you set off."
