Trevor Hamilton was convicted of Mrs Harron's murder in 2006.
The man who abducted and murdered retired librarian Attracta Harron in 2003 has had his whole life prison tariff quashed by the Court of Appeal.
Trevor Hamilton, 26, a farm labourer from Sion Mills, was jailed for life in 2006 for the Strabane woman's killing.
Judges ruled that Hamilton should instead serve at least 35 years before he can be considered for release.
But Lord Chief Justice Sir Brian Kerr stressed Hamilton may still spend the rest of his life in jail.
Mrs Harron, 65, from Strabane, was killed by Hamilton less than four months after he had completed a rape sentence.
She was last seen walking home from morning Mass in Lifford, County Donegal, in December 2003.
The body of the mother of five was found months later in a makeshift grave near Hamilton's home. She had been battered to death.