No, you must trade it from firered or leafgreen. Alternatively, if you have a gameshark or action replay, you can use codes to get him into your game.
No, he's not in your pokemon emerald game! But you can only catch him in firered/leafgreen you cant catch these legendary pokemon without a nintendo event, a firered/leafgreen game, or action replay: lugia, ho-oh, mew, mewtwo, celebi, deoxys, jirachi, the other latios/latias that you didn't have on your game, suicune, entei, raikou, and there are other to.
you can only catch him in firered/leafgreen to catch him in those games, you beat the elite 4 and then hes in the cerulean cave which is in cerulean city