By default Mirror's Edge has no editor executable like other Unreal Engine games like Unreal Tournament. However, with a little trick you can enable it to create maps.
Step 1: Opening the editor
To do so you will need to do two things:
1. Go to your Mirror's Edge installation directory (this is usually C:/Program Files/EA Games/Mirror's Edge/ ). Enter the Binaries folder and create a shortcut for the MirrorsEdge.exe . Open the shortcut's properties window and append the target line with " editor" (no quotation marks). If you have installed the game to the default location the shortcut target should be:
"C:\Program Files\EA Games\Mirror's Edge\Binaries\MirrorsEdge.exe" editor
(In case it doesn't work try it with "Editor" instead of "editor" in the end)
2. You need the WxRC and WxRes folders from another game with Unreal Engine. The confirmed games that have the files that are required to run the editor are Unreal Tournament 3 and America's Army 3 (you can get this one on Steam for free). You need to copy these two directories from the Binaries folder of those games to the Binaries folder of Mirror's Edge.
If you've done the 2 steps above you should be able to open the editor when running the shortcut.
Edit by Berthenk: the America's Army 3 files have been confirmed to only work with the Steam version. The non-Steam version of Mirror's Edge needs the files from Unreal Tournament 3!
Step 2: Editor basics
Now that you can open the editor, you can start making maps. However, due to the limitations of the editor, there are several things that you have to pay attention to in order to use it.
First of all you need to set up your Published and Unpublished folders, as you do NOT want to overwrite the original files. Go to %Documents%/EA Games/Mirror's Edge/TdGame . Create two new folders called Published and Unpublished if you don't have them already, then open them and create a CookedPC and inside it a Maps folder in both Published and Unpublished [needs rephrasing I think]. If you've looked around in the TdGame folder where you've installed the game you can see the same folder structure, which is no accident. Basically the folders you've just created serve the purpose of loading files in without modifying the original ones. What you have to know, is that when you run the game, and there is a file with the same name in the Published folder as in the installation directory, the game will load the one from Published (there are exceptions with packages, but save that for later). The same mechanic applies to the Editor and the Unpublished folder, so the editor will first try to load the file from the Unpublished folder.
When you open the editor, it will always start with an empty map, but you will need to save and load the map eventually, and unfortunately, the editor is restricted in this matter. The editor will only be able to open map files with names of the original files, what it means is, that you cannot save your map to whatever name you like, or you won't be able to open it the next time you run the editor. You can check the original map files for valid names, but for reference here is the list of names that are usually used: see list .
The editor will only look for the file it in the Unpublished folder, and if it can't find it, it will simply load the original files, so you must always remember to save (or copy) the map file to the right folder in the Unpublished directory.
If you've followed the two steps above you should have the required knowledge to start making your own maps. Have fun!