Belfast to Dublin airport

Belfast does have two airports (International and City), but at the moment I don't think you can fly to the US from either (they used to have direct flights from International to Newark), so you would need to connect thru somewhere like London. Or you could get the Aircoach directly from Belfast city centre to Dublin airport, which is less than two hours: https://www.aircoach.ie/

You can get a train from Belfast city centre to Dublin city centre but then you'd still need to get yourself to the airport.

Taking a bus from Belfast to Dublin Airport is fairly easy - about a 2 hour trip, frequent departures. The site https://www.transportforireland.ie is very helpful.
The train is also convenient but does not go to the airport, so involves transferring to bus or taking a taxi from Connolly Station.

Most of our tour group took the bus. The station was right next to the hotel. Very convenient. We took the train, which was also very convenient, but spent one final night in Dublin city center on Connolly, then on to the airport the next day via taxi.

Three bus companies run frequently from Belfast to Dublin Airport and Dublin- Aircoach, Dublin Express and Translink. Translink are the original and cheapest when booked ahead- they are the National public transport company of Northern Ireland. Dublin Express are the Irish arm of National Express in the UK.

We took the bus back to Dublin when tour ended. The bus stop was right next to our hotel. As with our other RS tours, our guide was very helpful at first group meeting. They’re a wealth of information and this is a frequently asked question.