Mr Armstrong went missing on his way to Mass in 1981 The funeral takes place on Saturday of Crossmaglen man Charlie Armstrong, one of the so-called Disappeared.
Mr Armstrong, 57, is believed to have been abducted, murdered and secretly buried by the IRA, nearly 30 years ago.
His remains were found at the end of July in County Monaghan near the border with Northern Ireland.
This week the Independent Commission for the Location of Victims Remains confirmed the remains were his after DNA testing was carried out.
Mr Armstong went missing on his way to mass in south Armagh in 1981.
In a statement earlier this week, the Armstrong family expressed their thanks to those who helped locate his body and said they now needed time to grieve.
Sixteen people were murdered by republican paramilitaries and secretly buried in isolated parts of Ireland during the troubles.
Seven bodies of the Disappeared have been recovered.
The commission set up to find the remains was established in 1999.
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