Do you need codmw2 single player to play multiplayer

Well, I don't know exactly what you mean, because both those playing options come in one disc. You'd need Xbox LIVE to play multiplayer online, but you could also play Co-op with Split-Screen, but if you want to play Co-op with people online, again, you need Xbox LIVE. Also, you don't need to finish the Single-Player Mode to play Multiplayer. I hope this answered your question.