Elite: Dangerous is available now on Steam, and those who already have the game can add it to their Steam library.
While it's pretty straightforward to add the game to your library, you can't actually add it as a Steam game unless it's purchased through Valve's client.
When the Mac version is available outside of beta, Steam users will be able to receive the game on Mac automatically. Elite: Dangerous is available for £39.99/€49.99/$59.99.
The game is also coming to Xbox One.