A happy reunion of (wo)man and dog occurred this morning at Pearse Street station after Patch arrived there on the morning commuter train.
Patch, a Jack Russell cross from Co Kildare had been missing since early yesterday evening. He boarded a train at Kilcock at 6.49am, arriving into the city centre before 8am.
Passengers notified staff when the train terminated.
A photo of Patch tweeted by Irish Rail was seen by his owner Deirdre Anglin shortly after 9.30am, after it had been retweeted over 500 times.
Irish Rail spokesman Barry Kenny - who described Twitter as a "a very effective alert-system" - said it took only 32 minutes for Ms Anglin to get in touch.
"It was a good job she showed up as they were getting quite attached to him in the office," he said.
Caroline Troy, station manager at Dublin Pearse, said the "new little member" was "very friendly" and that Irish Rail staff had named him Checker after the travelling ticket checkers onboard. "He almost got a little job," she said.
Ms Anglin, a fund accountant, was "absolutely delighted" to be reunited with Patch, who went missing at about 4pm yesterday.
"Myself and my sister then went on Facebook and asked people to share the photo so when I saw Irish Rail's tweet this morning, I was absolutely delighted and so pleased Irish Rail thought of using Twitter and the amount of times it's been retweeted."
Ms Anglin said Patch was almost a celebrity on the return train journey to Kilcock this morning, with other passengers enquiring if he was "the dog from Twitter".