Since 1) I’m getting a lot of hits for this at the moment (presumably because of my Crimes of RowlingGrindelwald movie review) and 2) I had to google the answer myself upon exiting the cinema, because the dang movie made me question things I thought I knew about the HP universe, let me lay the answer out right now and now, definitively.
As far as is canon in the HP books 1 – 7, no, Dumbledore didn’t ever teach Defence Against the Dark Arts. It’s specifically noted (I forget in which book, I used to reread them every July but haven’t in a couple of years now) that Dumbledore taught Transfiguration, and that when Riddle came to apply for the DADA job, the current occupant had been ‘teaching for fifty years’. It’s pretty clearly implied that that means teaching DADA for the last fifty years… But technically, the text doesn’t come right out and say that – so there have been some fans post-Crimes trying to reconcile things by suggesting that maybe that original bit from HP just meant that that professor had been teaching at Hogwarts generally for fifty years. Which, okay, sure, it fits the literal text… but it sure as heck doesn’t fit the implications.
And let’s be real: Crimes wasn’t exactly shy about breaking canon about other things, so it’s not really a stretch to assume that JK just decided to break canon and make Dumbledore the DADA teacher because….. reasons??
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Best I can reason, Dumbledore is the DADA teacher to give us all the excuse to a) see him in action while b) learning Important Tragic Things about Leta’s backstory i.e. see her Boggart, which (kind of?) opens up a mysterious subplot that ends up tying into Credence’s story in the end.
But… idk? I’m not convinced that was a good enough reason to break canon. Or, you know, bend canon like a contortionist.
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So, yeah, anyway. Final answer: No. Canon-Dumbledore never taught Defence/Defense Against The Dark Arts, but it’s possible to stretch canon dubiously to make it fit. Dumbledore teaching DADA doesn’t murder canon so much as simply torture it in a dark back alley.
I think we can all agree how I feel about that. 😛