Connecticut has become the 17th US state to abolish the death penalty, but the repeal will not affect 11 people still on death row.
The bill, signed into law by Governor Dannel Malloy, makes Connecticut the fifth state in as many years to end capital punishment, meaning one in three US mainland jurisdictions now outlaws the practice.
The legislation was introduced following the high-profile trial of two men sentenced to die for their role in a vicious 2007 attack on the home of prominent doctor William Petit.
Dr Petit was beaten with a baseball bat and tied up, while his wife was dragged off to a bank to withdraw money.
One of the assailants then raped and strangled her, while his accomplice raped the doctor's 11-year-old daughter.
The girl and her 17-year-old sister were tied to their beds, doused in fuel and left to burn as the intruders set the house ablaze and fled.
Mr Petit, still tied up, escaped to a neighbour's house and called the police.
The survivor and his sister Johanna had lobbied the Connecticut senate to vote against the bill, which replaces capital punishment with life imprisonment.
"Although it is an historic moment - Connecticut joins 16 other states and the rest of the industrialised world by taking this action - it is a moment for sober reflection, not celebration," Mr Malloy said in a statement.
"In the last 52 years, only two people have been put to death in Connecticut - and both of them volunteered for it.
"Instead, the people of this state pay for appeal after appeal, and then watch time and again as defendants are marched in front of the cameras, giving them a platform of public attention they don't deserve."
He said the remaining Connecticut death row inmates "are far more likely to die of old age than they are to be put to death".
According to the Death Penalty Information Center, Connecticut has carried out only one execution since the re-establishment of capital punishment in the United States in 1976.
Four other states - Illinois, New Jersey, New Mexico and New York - have dropped the death penalty in the past five years, while California plans to hold a referendum in November.