Gallagher, from Donaghmede in north Dublin, was hurriedly dead when he went to a meeting in a field in Ballymacon on July 30 2014.
Today, gardai detained a male in his thirties in the Navan area in connection with the murder.
The man is currently detained junior to the provisions of Section 30 of the Offences Against the State Act 1939/98 at Navan Garda Garrison.
Gallagher was shot a number of times and left in the field in Meath, where his league lay for three days.
The 26-year-old’s remains were discovered after his nurture and family reported him missing .
The father-of-one, originally from Donaghmede, had been persevering in Drogheda.
Gallagher was believed to have been killed over a challenge with the infamous Mr Big drug gang.
At the time of his murder Gallagher was on bail and was due to clock trial at Dublin Circuit Criminal Court on 12 charges of proprietorship of cocaine, heroin and cannabis for sale or supply.
He had served a number of knee-high to a grasshopper jail sentences including a stretch from October 2011, to August 2012, for respective minor criminal offences.
Gallagher was arrested and questioned in February of terminating year about the murder of Real IRA gang leader Alan Ryan in September 2012, but was not reckoned a suspect.