A West Virginia judge has denied Ireland's request to extradite George Exoo, a Unitarian minister charged with assisting the suicide of Rosemary Toole in Dublin five years ago.
After reviewing assisted suicide laws in all 50 US states, Magistrate Judge R Clarke VanDervort concluded that Ireland's extradition treaty with the US does not support extradition for Mr Exoo on the assisted suicide charge, which carries a sentence of up to 14 years in prison.
"While Mr Exoo's conduct may be viewed as wrong, it is generally not recognised as criminal in the United States," Mr VanDervort said.
Rev Exoo (64) was immediately released from jail, where he had been held since prosecutors began extradition proceedings in June and was celebrating last night with friends.
Outside the jail in Charleston, West Virginia, Rev Exoo praised the ruling.
He has claimed that, although he was with Ms Toole when she died in her home in Donnybrook, in 2002 and offered advice on how to ensure that her suicide would be successful, he played no active part in her death.
Ireland's extradition treaty with the US covers only offences "punishable under the law of both contracting parties by imprisonment of more than one year".
Assisting a suicide is not a crime in West Virginia or under US federal law, but prosecutors argued that, if Rev Exoo's alleged actions are a felony in most US states, he should be extradited.