Rent a car in Dublin and drop off in London?

Yes, it's possible. https://www.hertz.ie/rentacar/reservation/

Beware of high international drop off fees.

Make sure the rental car company allows the car to be taken on a ferry - some don't or add a surcharge.

Just because you can doesn't mean it's a good idea. I have a feeling that once you price it, you will find other options more attractive.

Extra costs:

1. The cost to transport a car on a ferry. I have not priced that route specifically, but I bet it's not cheap.
2. The (probably very high) fee for a one-way "drop off" in another country. Check with the rental agency and ask specifically what that drop-off fee is, maybe shop around...but I suspect all will be cringe-worthy.
3. Driving in London? Yikes.

Consider alternatives.

Four years ago, we rented in Galway and dropped off at Dublin airport (I don’t recall now whether is was from Europcar or Enterprise) and it was easy, and I don’t believe there was any extra fee. Dropping off a different city in the same country is no big deal.

Twenty years ago, three of us rented from Hertz, picking up in Lisbon, Portugal and dropping off in Malaga, Spain. That was convenient, but we all split the $600 multi-country extra fee. There was no ferry charge on top of the rental fee and the gas it took to drive there.

Would a better option be to rent a car in Dublin, drop off in Dublin, take the ferry to Holyhead. Then rent a different car in Holyhead and drop off in or near London? This is my first trip going from Ireland to England in the same trip, so I'm open to recommendations! Flying into Dublin and leaving from London. Thanks!

Do you plan to visit North Wales? Why would you need a car in Holyhead otherwise? There is a train station there with good connections towards England.

The only reason why I'll be in Holyhead is to depart the ferry. My next stop from Holyhead is in the Yorkshire Dales area (northern England). If there is a train from Holyhead to England, where would be the best place to exit the train and obtain a rental car?

what about flying from Dublin to Manchester (or Leeds/Bradford) then you can hire a car at the airport and explore the dales?

tell us your overall plans so we can best advise.

Yep, what ramblin' on said above.

There are an infinite number of ways to get from place to place. The optimal choices in getting around depends on multiple factors, including time, budget, personal tastes, and most of all, how all that gettin' around fits into your larger goals. So share you agenda, your overall plan, and what you are hoping to do/see (as well as your taste preferences, and the time you have).

That's a great idea. Flights are super cheap from Dublin to Manchester. My goal is to get from Dublin to Skipton, UK on 3/22. So I'd like a car to travel to Skipton, then around the English countryside for a few days, ending up in London.

I truly appreciate everyone's suggestions. The last time I was in the UK was 1999, when there were no cells phones and the internet was in its infancy! Wow that makes me feel old. The car rentals have gotten much more strict since then.

Between the proliferation of super-cheap flights, and the great availability of rail transport, it's surprisingly easy to get around most parts of Europe these days. In your case, it sounds like a cheap flight from Dublin to somewhere near your real destination (Manchester, Leeds, York) would put you within striking distance. Rent the car there, enjoy more time where you want to be.

Personally, I would drop off the car somewhere close to wherever you are when you no longer actually need it, then take the train to London. London and cars do not mix well.

To search for cheap flights, use Skyscanner -- it will show the budget airlines that don't show up in Kayak or Expedia or whatever.

If you do end up on a budget airline, pay close attention and adhere to the baggage rules.

Thanks everyone for your suggestions. I ended up getting a flight from Dublin to Manchester and will take it from there!

good news on the flight.

Don't even think of driving the car to London. Maybe Heathrow or Luton airport but no further. There are now 3 overlapping different daily fees totalling around £50 a day to drive into London.

As others say, as soon as you don't need the car (leaving the beautiful Yorkshire Dales maybe???) you can get the train very easily and much faster.... plan ahead and it can even be cheap...