Illinois has this week abolished the death penalty and pulled 15 inmates off death row.
A slew of wrongful convictions over the past decade led to a moratorium on capital punishment in the midwestern US state.
The move is expected to help spur lawmakers and courts in some of the 34 US states with capital punishment still on the books to follow suit.
'This is a state that used the death penalty, reconsidered it and now has repealed it,' said Richard Dieter, executive director of the Death Penalty Information Centre.
'That's different than a state that hardly ever used the death penalty and decided to get rid of it.'
Six states - Connecticut, Florida, Kansas, Maryland, Montana and Washington - are currently considering bills to abolish the death penalty and moratoriums are currently in place in several others.
'For me, this was a difficult decision, quite literally the choice between life and death,' Illinois Governor Pat Quinn said after signing the bill into law.
Mr Quinn said he has determined that 'our system of imposing the death penalty is inherently flawed' and that there is 'no credible evidence' that capital punishment deters crime.
The Illinois Governor had long been a supporter of the death penalty.
12 executions since 1976
Illinois has carried out 12 executions since 1976, when the Supreme Court reinstated the death penalty, according to the Death Penalty Information Centre.
In the same period, 20 inmates have been exonerated from the state's death row, the second highest number in the US.
'As a state, we cannot tolerate the executions of innocent people because such actions strike at the very legitimacy of a government,' Mr Quinn said in a statement.
'Since our experience has shown that there is no way to design a perfect death penalty system, free from the numerous flaws that can lead to wrongful convictions or discriminatory treatment, I have concluded that the proper course of action is to abolish it.'
Illinois helped spur a national debate in 1999 after a group of students at Northwestern University were able to prove that a death row inmate was, in fact, innocent.
Then-governor George Ryan imposed a moratorium on the death penalty in 2000 and three years later commuted the sentences of 167 death row inmates to life in prison.
Since then, 15 people have been sentenced to die in Illinois, but none have been executed.
Those sentences were commuted to life in prison without the possibility of parole by Mr Quinn, who took nearly two months to reach a decision celebrated by death-penalty opponents.
'By repealing the death penalty, Governor Quinn and the Illinois legislature have taken an historic stand against the systemic injustices that plague the entire death penalty system in Illinois and the rest of the United States,' said John Holdridge, director of the American Civil Liberties Union's Capital Punishment Project.
'Executions in this country are carried out as part of an unequal system of justice, in which innocent people are too often sentenced to death and decisions about who lives and who dies are largely dependent upon the skill of their attorneys, the race of their victim, their socioeconomic status and where the crime took place.'
Some 138 people sentenced to die have been released from death rows across the US with evidence of their innocence since 1973, according to the Death Penalty Information Centre.
However, support for the death penalty remains relatively high.
Support for death penalty
Some 64% of Americans say they are in favour of the death penalty for people convicted of murder, while just 29% oppose it, according to Gallup's annual crime survey.
That's down significantly from 1994, when support for the death penalty peaked at 80%, but still well above the all-time low of just 42% support.
When given a choice of sentencing murders to the death penalty or life in prison with no choice of parole, support for the death penalty fell to 49% of Gallup's respondents.
There has been a steady shift away from imposing the death penalty at the judicial and legislative levels, and the number of death sentences imposed has fallen by more than 60% since the mid 1990s.
A dozen US states and the capital Washington did not reinstate the death penalty after it was briefly banned by the Supreme Court in the 1970s.
New York reinstated the death penalty in 1995, but it was overturned by the state's courts in 2004. New Jersey abolished the death penalty in 2007 and New Mexico voted to abolish capital punishment in 2009.
A total of 1,242 people - about a third of them in Texas - have been executed in the US since the death penalty was reinstated in 1976.