Yes, you will need to register.
I flew my
Mini3Pro with Plus batteries last summer in Dublin & nearby area. I registered my aircraft with the Irish Aviation Authority and I was in full compliance with their weight/class regulations at that time. You will also need to take their operator's test (open book -- similar to U.S. FAA TRUST test)
Be sure to check the Irish Aviation Authority's site for current drone regulations as things tend to change at start of a new year (not saying they've changed, but best to be sure).
As mentioned by OMM, Ireland is under EU regulations, so you can actually register at any EU country. There is a minimal registration fee if you register with the Irish Authority. Some EU countries didn't charge a fee (as of last summer). I also flew in the Netherlands with no issue although there are far more no-fly zones in the Amsterdam area.
There's some really beautiful flying locations in Ireland.
Good luck!