How to Get from Nafplio to Athens Airport?

Driving from ATH to Nafplio and back again was easy driving on a modern highway and then some rural roads in the Nafplio area. I actually hate cars and driving, but I cannot think of any reason to not drive on this route, especially given the freedom it provides. You can stop at Corinth/ArcoCorinth, Nemea, plus easily visit sites in the vicinity of Nafplio. If you drove in Ireland (I've ridden along there too--lucky to have a good driving partner like you), so I assure you further--you got this. We booked an apartment with parking that was up above the old town a bit--easy to enter town and park, easier to walk down for dinner.
I did a quick check on RometoRio, which is far from exhaustive, but it looks like you would have to change buses in Athens. You could probably book a private driver that would not break the bank, but I think that is money better spent on a rental car.

Once you are in Napflio you will want a car to to visit the antiquities that surround the city- Mycenae, Epidavros, Tyrins, Nemea. etc.

Of course there is public transportation available. Coaches from Nafplio to Athens, and train or metro from there to the airport.

There is no bus from the airport that goes direct to Nafplio.

You'll have to go to the main bus station in Athens on Kissifou St. which means taking either a taxi or bus to the bus station and then wait for the bus to Nafplio which about 2-2 1/2 hours.

There are private transfers which can be pricey but will be much quicker and straight to Nafplio. This one is very reliable but cost about 150 euros. If there is more than one person you can share the cost. https://www.greek-taxi.gr/

Renting a car at the airport will be convenient and you'll need one in Nafplio to see the sites/sights anyway.

The bus back into Athens from Nafplio stops at Eleonas metro station. That’s on the direct line to the airport and the metro journey takes about 50 minutes. There are two trains an hour to the airport.

We’ve done this a couple of times and it’s easy and reliable.

Alan

I took my daughter to Greece two years ago and the first part of the trip was Athens Airport to Napflio and back for 4 days. I looked for public transportation too but it seemed time consuming and not direct. So decided to rent a car. I was nervous, but It was really very easy so I would encourage you to rent a car. I also used the local company, Athen Car Rental, I think? because of the insurance, they were great. They meet you on arrival, show you to your car, you exit the airport and you are on a modern expressway. Because I was also a little skittish, I planned everything out. I looked up the prices of the tolls beforehand and separated the money out, even though it was easy enough at the booth to get change. In Napflio we had a hotel in town, so we parked in the very large free lot near the docks that always had space, easy peesy. We used the car to drive to take day trips to the local sites, which was also very easy with a gps. Drove back to Athens airport and dropped off right at the curb.

I've always rented a car and driven around Greece. I used to also rent a GPS device for the car but now I use my iPhone and Google Maps as my GPS. Works great and it's an easy drive to Napflio.

If you decide to go by bus the timetable is here. The link looks weird but it works!

https://www.ktelargolida.gr/%ce%b1%ce%b8%ce%ae%ce%bd%ce%b1-%ce%b9%cf%83%ce%b8%ce%bc%cf%8c%cf%82-%ce%bc%cf%85%ce%ba%ce%ae%ce%bd%ce%b5%cf%82-%ce%ac%cf%81%ce%b3%ce%bf%cf%82-%ce%bd%ce%b1%cf%8d%cf%80%ce%bb%ce%b9%ce%bf/