Xerinola said:
I think that if it like this: "It was performed at the Palais Garnier, the Opera House named after the architect Charles Garnier."
If it like this, it's not necessary because "the Opera House named after the architect Charles Garnier" is an explanation and you already put the comma after "at the Palais Garnier".
This is my opinion!
I probably should've kept part of my post.
The way to tell if you need a comma is
first to know whether Charles Garnier is the architect of the Opera House or if he is just some architect after whom it was named.
Second, rewrite the sentence leaving out "Charles Garnier." If he is the architect of the Opera House, then the sentence should still make sense. If he is not, then the sentence should seem ambiguous. Now put his name back into the sentence. If it made sense without his name, you need a comma; if it made no sense and was ambiguous, you cannot have a comma.
Assuming Charles Garnier built the Opera House:
It was performed at the Palais Garnier, the Opera House named after the architect. [makes sense, even though if you really wanted to leave out his name, you should say, "...after its architect..."; nevertheless, the reader infers that "the architect" is that of the Opera House, and there is only one of him...so NOT ambiguous]

comma needed
It was performed at the Palais Garnier, the Opera House named after the architect, Charles Garnier.
Assuming Charles Garnier did NOT build the Opera House:
It was performed at the Palais Garnier, the Opera House named after the architect. [what architect? ambiguous! therefore, we canNOT use a comma]
It was performed at the Palais Garnier, the Opera House named after the architect Charles Garnier.
Hope this helps.
Brian