UPDATE: Multiplayer Confirmed In Mass Effect 3
UPDATE: Early details on Mass Effect 3's newly announced multiplayer mode have started to slip out via the developer's forums.
According to the forum post, the multiplayer mode will be cooperative with up to four players. Players will be able to "choose from a variety of classes and races," and success in the co-op mode will affect the "Galactic Readiness" system in the solo game. It's unclear how that will influence your game overall, but knowing BioWare and the Mass Effect series, it could be a primary factor in deciding how the universe looks when you finish Mass Effect 3.
ORIGINAL STORY: Commander Shepard has never been the go-it-alone type, but the hero will have more backup than usual in Mass Effect 3. Confirming longstanding rumors, BioWare has revealed that the third installment of the series will feature an online multiplayer component.
Details on Mass Effect 3's multiplayer functionality will be appearing in the November issue of Australian mag PC Powerplay. Details are scarce at this point, but Eurogamer is reporting that multiplayer is separate from the main campaign and will include some form of competitive element.
We'll have more information on Mass Effect 3's multiplayer soon, so stay tuned.