I have never played Mass Effect: Pinnacle Station, but it no longer appears to be available on Steam. This DLC now only appears to be available on Origin, from what I can see.
I own Mass Effect on Steam, but the Steam CD key for the first Mass Effect game is not valid within Origin (the CD key for Mass Effect 2 is, but that's not going to help in this particular situation).
Am I able to purchase Mass Effect: Pinnacle Station on Origin and then use it with my copy of Mass Effect from Steam, or am I going to need to repurchase Mass Effect on Origin in order to use the Mass Effect: Pinnacle Station DLC, from Origin?
Best Answer
In many cases for EA games you can use the key from Steam to also get the game on Origin. This is an automated process, meaning it is quick and can be done at any time, but doesn't work for all games. If this doesn't work you can consider using Origin support and hoping for the best. You can also just buy the DLC and hope for the best, it may still work. But actually getting the game you bought on Steam to show up as owned on Origin is the safest way to ensure that the DLC from Origin will work.