Kevin Murray, 47, was wanted in connection with the killing of David Byrne in February last year.
But extradition proceedings were ended at Belfast Recorder’s Court due to Murray being diagnosed with rapidly deteriorating and terminal motor neuron disease.
Her Honour Judge Patrica Smyth ruled: “I’m satisfied the only appropriate course I can take is to discharge the requested person.”
Byrne, 34, from the Crumlin area of Dublin, was shot dead at the city’s Regency Hotel.
Linfield v Portadown Sunday clash: Breakers of the Sabbath will answer to God
College lecturer dies while on holiday
Tom Topping: Heartbroken daughter says ‘world is totally shattered’ after father’s shock death - funeral details released
Michelle O’Neill has kicked sand in the face of victims of terrorism
‘Holistic and inclusive’: Northern Ireland Office Wilton Park report so full of ‘lazy jargon’ it makes you ‘lose the will to live’
Masked men dressed as Garda officers opened fire with automatic guns during a boxing weigh-in at the venue.
The murder ignited a deadly feud between members of the rival Kinahan and Hutch gangs.
Murray was detained last September under a European Arrest Warrant issued by authorities in the Irish Republic.
He was being sought for alleged offences of murder, possession of a firearm with intent, and possession of a firearm in suspicious circumstances.
It was previously claimed in court that he had stayed overnight at the hotel in preparation for his alleged role in the shooting.
Gardai investigating the killing allege Murray can be clearly identified on CCTV footage and photographic evidence.
Another man, 25-year-old Patrick Hutch of Champions Avenue in Dublin, has been charged with the murder.
He is alleged to have acted with the Co Tyrone man as part of the same gang.
Lawyers for Murray opposed his extradition by claiming it was unlikely he would ever stand trial because his motor neuron disease is so severe.
They argued that would be unjust and oppressive to send a man receiving end of life care to the Republic.
Medical opinion backed their contention that his condition was rapidly worsening and will lead to eventual death.
Murray is completely bedridden, suffering from respiratory difficulties and being fed through a tube, the court heard.
He is unable to converse and has limited power in his arms and legs.
Counsel for the Irish state accepted that his extradition is currently barred, but sought a three-month adjournment to see if there is any improvement in his condition.
However, Judge Smyth held: “It’s clear from the doctor’s report of March 2017 that the requested person is dying of motor neuron disease.”
Confirming the decision to discharge Murray, she acknowledged he was being sought for prosecution over a murder and said a fresh extradition application could be made if medical opinion changes in future.