No, never. He works as an auror, but aurors can't cast killing curses.
- In the movie (maybe the book?), Harry Potter and the order of the phoenix, Harry attempts to cast Avada Kedavra (Killing curse) upon Bellatrix Lestrange because she contributed to Sirius' death. However Harry can't cast the curse correctly as he is a good person and to use that spell, you've got to mean what you say.