Sligo to Fishguard

The ferry departs Rosslare at 08:00 and 18:10

The 18:10 departure works well for a same day journey

Depart Sligo 09:00 arriving Dublin Connolly 12:01 - time for a leisurely lunch and
Depart Dublin Connolly 13:36 arriving Rosslare Europort 16:28 - the station appears to be right at the ferry terminal.

Minimum checkin time is 30 minutes - so even if the train was late, should have plenty of time

The ferry is due into Fishguard at 21:25


On the way back the ferry departs Fishguard at 13:10 and 23:45

The 13:10 departure arrives into Rosslare at 16:25

There is a train departing at 17:40 or 17:50 on Sundays which arrives into Dublin Connolly at 20:51
Every other day it departs at 18:00 arriving into Dublin Connolly at 21:00

The last train to Sligo departs at 19:05 - so an overnight stay in Dublin would be required

The other option would be to stay overnight in Rosslare, and get the train the next morning - which would take about six and half to seven hours to Sligo.

It's worth searching the web for Stena discount codes - at the time of writing there's a 25% discount available - MELTING25

Stena also have their own "day out" fare from UK to Ireland which makes it cheaper to book a day return from the UK to Ireland for the inbound leg