Maximum prison sentences in England and Wales for allowing a dog to fatally attack someone have increased from two years to 14 years, while the term handed down when injury is caused is up from two years to five.
For the first time, the Dangerous Dogs Act also includes a specific offence to protect assistance dogs, such as guide dogs, from attacks, with guilty owners facing up to three years in prison.
Two babies were killed by dogs earlier this year.
Six-day-old Eliza-Mae Mullane was mauled by a family pet in Pontyberem, South Wales, in February. Less than two weeks later, 11-month-old Ava-Jayne Corless was killed by a pit bull terrier in Blackburn.
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Defending the amended law, Animal Welfare Minister Lord de Mauley said: "Dog attacks can have horrific consequences for victims and families and it is only right those responsible should face tough punishments.
"This will give protection to those who provide vital services in the community - postal workers, nurses, utility workers - as well as people visiting family and friends."
Guide Dogs chief executive Richard Leaman said: "An attack on a guide dog can be devastating. It can rob someone with sight loss of their independence and freedom, leaving them virtually housebound.
"We're delighted that irresponsible owners can now be given tougher sentences if their dog attacks an assistance dog.
Trevor Cooper, from the Dogs Trust, said he hoped the changes would encourage owners to be "more cautious", but said tougher sentences were "not the solution".