Patch was discovered unaccompanied on a train shortly after it left Kilcock station in County Kildare early on Wednesday morning (July 4), and was handed over to Irish Rail (Iarnród Éireann) staff when the service arrived at its destination in Dublin.
Irish Rail used its Twitter account to post a photograph of the dog along with the message: "Lost dog! Boarded at Kilcock at 06.49 this morning, currently being looked after in Pearse Stn. Please retweet."
Patch's owner Deirdre Anglin contacted Irish Rail half an hour later, following almost 500 retweets of the original message. The dog had gone missing from her home on Tuesday afternoon (July 3).
Anglin told the Irish Sun: "When I saw Irish Rail's tweet, I was absolutely delighted and so pleased they thought of using Twitter."
An Irish Rail spokesperson told BBC News: "We are delighted to have played a part in reuniting Deirdre and Patch. Patch seemed to enjoy his adventure, and was a very friendly dog.
"We also want to thank our customers on the train, and our Twitter followers - it was a great team effort, and testament to the power of Twitter."