The offer is part of EA’s new Origin Game Time initiative. You need to make the most of the time however. Your 48 hours of free play begin when you first launch the game, but the timer ticks down whether you’re playing or not.
EA explained on the Origin blog that Origin Game Time games will appear on the Free Games page when they're available to download. If you enjoy the game and decide to purchase it afterwards your progress and unlocks will carry forward.
EA added, “Titanfall is only the beginning for Game Time and there's more on the way," EA concluded. "Each Game Time will be unique: different game, different time on the Game Time clock."
Alternatively, if you’re in the mood for something more chilled, you can get your hands on the rather excellent Peggle for free as part of Origin's latest monthly On the House offer.