Nope, and Yes. Nope = All snakes in Ireland died in the last ice age, and no new ones have made it across the (really cold) Irish Sea to set up shop again. Yes = There are venomous snakes in Ireland now, but they were exotic pets that were abandoned -- however none are loose since the zoos and authorities have all of them.
From an article entitled "List of reptiles in Ireland."
There is only one land reptile species native to Ireland, the viviparous or common lizard. It appears to have a widespread distribution across the entire island with coastal, bogland and mountainous areas showing highest numbers of sightings. A legend tells that Saint Patrick banished all snakes from Ireland, but in reality there is no suggestion that snakes ever existed in Ireland.