Portal 2

The requirements for this are simple enough, though you cannot quit, or complete sections of the course to earn this achievement. It has to be done in one sitting.

If you're having difficulty mastering each chamber, hopefully the video below will help solve any issues.

The following time markers are the start of each chamber:

Chamber 1: 00.10
Chamber 2: 00.58
Chamber 3: 01.55
Chamber 4: 03.19
Chamber 5: 05.25
Chamber 6: 06.52
Chamber 7: 08.19
Chamber 8: 09.45
Chamber 9: 12.27

Chamber 8 contains a rather simple but tricky funnel maze with crushing panels. Just take it slow and communicate non stop. On the last upward funnel section allow your partner to time the funnel jump. Jumping on and off of the reverse button may cause confusion and death.

Here's another solo run through this achievement. This one has a commentary throughout and avoids the hard part of chamber 8 by skipping it completely.

Edit: Thanks to Predator Ranger for pointing this out.
While I did do it in Chamber 9: you do not need to bring the blue guy through to the end. Once you get the first guy to the end he can put in the disc and finish the level. Both players will unlock the achievement. This eliminates the dangerous part of going through the conveyor belt twice.

You must complete all of Course 4 (all 9 chambers) without you or your partner ever dying. You must start from Chamber 1. If you or your partner die, you must restart from Chamber 1. The achievement will pop soon after you insert the disc into the player.

In my opinion, the last two chambers are really the only ones that may give you issues without preparation. Chamber 8 has the "spike maze," be sure the one inside is quick with the portal gun and the one outside is quick with the button. In Chamber 9, be sure the person controlling the light bridge covers all your tracks so a stray turret doesn't kill you. I recommend playing through these last two chambers until you and your partner are comfortable with the puzzles before starting this achievement.

If you have everything fairly memorized, the entire course should only take about 20 or 30 minutes to complete.

Hi, I don't have anything to add other than I used the following video to do this alone (the guy in the video does it alone as well which makes it very easy to follow along with) without too much of a problem. The only place I died the first time I tried it was in chamber 8, and that was a foolish mistake. I would suggest that you load up chamber 8 and do a run through of that alone using this video if you are going to do this, and work out the kinks there.

This is a heads up -
Do NOT set the DLC to download and decide to attempt a run of Still Alive (in my case solo) while waiting.

Once the download completes a confirmation will pop up, only giving an option to accept resulting in "exiting" to the main menu and thus all progress lost.