If you're looking for a meeting place or a good stop around ½ or halfway between Carlow and Ballyshannon, you can try Kells, Ireland, which is about 1½ hours north of Carlow, or almost 2 hours southeast of Ballyshannon.
About ¼ or a fourth of the way, you can stop at Blanchardstown, Ireland. This is almost an hour northeast of Carlow.
About ⅓ or a third of the way, you can stop at Maynooth, Ireland. This is about 1 hour north of Carlow.
About ⅔ or two thirds of the way, you can stop at Cavan, Ireland. This is a little over 2 hours north of Carlow, or about 1 hour southeast of Ballyshannon.
About ¾ or three fourths of the way, you can stop at Belturbet, Ireland. This is about 2½ hours north of Carlow, or almost an hour southeast of Ballyshannon.
If you drive straight through without stopping at all, the total distance is 276 km. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 3 hours, 18 minutes.