http://www.gamingunion.net/news/mirrors-edge-took-7-years-to-make--1115.html
Gaming Union: What do you think of DICE's choice to make Mirror's Edge, and now that they're developing a sequel?
Liliegren: Knowing that that product was in development for about seven years.. [laughs] and given that it wasn't Mirror's Edge when we started, but it was one team working on 'the new IP' for seven years, I think they did a strong final. They did something different that people hadn't done before. I think it needed a second generation so they can tweak on it, I played it a little bit.
Wow, I would have guessed 2-3 years.