“The death penalty is the ultimate form of punishment and the ultimate tool for punishing others,” said Andrew Cuomo, New York governor, who signed a new law on Thursday making it a death penalty offense.
“I’m sorry if you’re feeling anxious about what that means, but it’s not going to change your life, and it’s certainly not going for me.”
Mr Cuomo is the first New York mayor to sign a death sentence, following the death of a former governor, Antonio Villaraigosa, in February.
“We are a nation of laws and I’m a firm believer that no man is above the law,” Mr Cuomo said.
Mr Cuomo’s bill, signed by the governor in Albany, will take effect in less than two weeks.
It is the latest in a string of measures in New York to toughen penalties for the capital offence of murder.
New York has the most executions in the US and the highest rate of executions in Europe, with more than 80 in all.
The state has also become the only state in the country to have its death row population reduced in recent years.
In April, New Jersey became the first state to abolish capital punishment, with Gov Christie calling it “the wrong way to go” and “a moral disaster”.
The governor’s announcement followed the killing of former New York City mayor Rudy Giuliani by New Jersey State Police officers in November.
He had been accused of sexually assaulting a woman at a charity event.
The death penalty has long been a divisive issue in New Jersey, with Republicans calling for a moratorium on executions until the death penalty can be abolished in the state, while Democrats say it is cruel.
Mr Christie’s decision to sign the bill, a move he said would help make New Jersey “a leader” in the nation’s capital, came less than a week after a New York jury found Mr Giuliani guilty of manslaughter in the killing and acquitted him of the murder.
In May, New Yorkers voted to abolish the death sentence for murder.