Pet shops and dealers in England will be banned from selling puppies and kittens under government plans.
The proposals, which have gone out to consultation, will mean those wanting to buy or adopt a pet less than six months old will have to go to the breeder or a rescue centre.
A ban on licensed sellers dealing in dogs and cats less than eight weeks old is already coming in on 1 October.
Campaigners welcomed the announcement, but warned of "potential loopholes".
It is a victory for the Lucy's Law campaign, which has been calling for the ban to be implemented.
The campaign was named after a Cavalier King Charles Spaniel who was badly treated in the puppy farming system.
The ban aims to reduce the health problems associated which emerge when animals are reared in poor conditions.
There are no records of the number of puppies sold via third parties, but the animal charity Blue Cross has estimated it is between 40,000 and 80,000 per year in Great Britain.
The Department for Environment, Food and rural Affairs said fewer than 100 third party sellers - which includes some pet shops - are licensed in England.
Speaking in support of a change, Environment Secretary Michael Gove said: "People who have a complete disregard for pet welfare will no longer be able to profit from this miserable trade."
The move was welcomed by Paula Boyden from the Dogs Trust - but she warned that "potential loopholes" needed to be closed off for the ban to be successful.
"We believe that to be effective, a ban needs to be supported by some key additional measures, such as regulating re-homing organisations," she said.
Caroline Kisko, Kennel Club secretary, said the ban would "stop the suffering of many dogs and send a very strong message to puppy buyers that it is never OK to see a puppy in any environment other than the one it was born and raised in, and with its mum."
Marc Abraham, of the Pup Aid campaign, said: "Irresponsible breeders have for years used third parties to keep themselves hidden from the buying public and the proposed ban will make all breeders accountable."
Picture: Pupaid Twitter page