Mr Charlton, 48, died at home in Frosses on Saturday evening last after a long battle with cancer.
The serving Garda, who had been stationed at Glenties station, will be buried after funeral mass at St Mary’s Church in Frosses at noon.
Chief mourners will be Ms Coughlan and the couple’s two children Meabh, 15 and Cathal, 13.
Hundreds of people have called to the family’s home over the past two days to pay their respects to the late Mr Charlton.
A native of Kiltimagh in Co Mayo, Mr Charlton met Ms Coughlan while on duty at Dail Eireann more than 20 years ago.
Among those expected at the funeral will be former Taoiseach Brian Cowen, current Fianna Fail leader Micheal Martin and MEP Pat The Cope Gallagher.