Like how the US Bill of Rights doesn't have a "the" in front. Something like this: http://theeasterrising.eu/220CivilWar/jpg/Constitution.jpg
We apply different rules in English when we are creating the title of a book or some other work - for example we typically capitalize each noun, and we can drop an initial definite article. So you can't draw a simple conclusion by comparing a title in English and Irish. For example, the correct title of William Golding's work is "Lord of the Flies", but Tolkien's collection is called "The Lord of the Rings". In Irish those titles are Tiarna na gCuileog and Tiarna na bhFáinní, even though there is a leading "The" in the second title.
Unless you can come up with an ordinary circumstance where you would say "Constitution of Ireland" without a definite article, (or quotation marks"), then the circumstance doesn't arise where you need to need to understand how to translate it.