Wee done this one as a loop with slieve croob, slivenisky and cratlieve.
We went up through the forest to stay off people land. View from top is great. We parked at slieve croob carpark Linkback: https://mountainviews.ie/summit/1068/comment/21507/

Armed only with the knowledge that three very illustrious Summiteers had managed an ascent before me, I set out to discover a route to the top of Slievegarran on a glorious spring evening. A drive around the northern perimeter revealed a lot of farmland and a forestry plantation festooned with forbidding notices aimed at anyone interested in trespassing or shooting. I chose to start from the minor road to the east at (323424 A) (room to squeeze a car or two onto the verge) where it seemed that just the one fence separated me from relatively open hillside.

From this point a subsidiary ridge runs roughly parallel to Slievegarran's main ridge (i.e. NW-SE) and I headed straight up to it. Once you meet the crest of that lesser ridge you can turn straight up it until in sight of the plantation, but you can save a little effort by contouring its far slope above a boggy hollow. Said hollow is easily crossed just short of the plantation, and then a steep but straightforward slope of grass leads to the summit area. There is no higher ground between here and the Mournes to the south, hence the views are really rather good.

See track 2467. Linkback: https://mountainviews.ie/summit/1068/comment/16017/