Pretty straightforward achievement. Simply play two hours, cumulatively, of the Sector Control multiplayer mode. This does not have to be done in one session. Sector Control is a capture the flag variant. There are typically three flags to control, and respawns are unlimited. At the end of each round, the statistics shown on-screen include the match time, if you want to keep track. In my experience, these matches typically take about 6-7 minutes each. So you will probably have to play approximately 17-20 rounds of Sector Control to earn the achievement. It will pop in the middle of the match as soon as you hit your two-hour mark. Afterwards, you can continue the round, or quit if you choose to do so.
Edit: If you have any suggestions for improving this solution, please leave a comment. Sorry, there is no known shortcut for doing this in less than the required time, but I tried to include as much helpful information about the match-type as I could.