Merseyside Police said the dog was destroyed following the incident in Richard Kelly Close, Clubmoor, at 20:40 BST on Saturday.
Two women, aged 27 and 28 and from Clubmoor, have been arrested on suspicion of an offence under the 1991 Dangerous Dogs Act.
A post-mortem examination on the man’s body is due to take place later.
Merseyside Police said the dog was out of control when officers arrived at the house and found the injured man in the garden.
He was later pronounced dead in hospital. The breed of dog has not been confirmed.
The women have been arrested under the section of the Dangerous Dogs Act that relates to an owner or a person in charge of the dog allowing it to enter a private property where it is not permitted to be and the animal injures a person.