He was detained in Jonesborough, Co Armagh on Wednesday morning.
Police also searched a property in the area.
The man has been taken to Antrim Serious Crime Suite for questioning.
Mr McCartney, a 33-year-old father of two from the Short Strand area, was attacked after he became involved in a row in Magennis's Bar in the city centre.
He was beaten and stabbed outside the bar and later died in hospital.
His sisters, who have accused republicans of covering up the killing and intimidating witnesses, launched a campaign for justice which took them to the White House.
To date no-one has been convicted but senior republican Pádraic Wilson was charged with IRA membership as part of the murder probe.