Can be obtained in Private Matches (versus bots included). Campaign XP counts too.
You will have to gain 150 total levels and re-up 3 times in order to gain this. Experience to level up is gained through pretty much all game modes. As you progress you do also get Reward Boxes that give you XP sometimes. The standard is 200xp which is nothing great as far as a reward goes. There are special times when you can get more experience when you play. This would include special events, promotional offerings, and Micro Transactions. You may purchase Double XP for a certain amount of matches which you can check in your stats screen. You can also purchase the VIP pass which grants you a VIP game mode that allows you to get double XP. Therefore the fastest way to level up, is to spend extra money to get more experience as you play.
Warning: The game counts the tickets even if you join in the middle of a match. That means, if you join and the game has 2 minutes left, you basically get ripped off a ticket. It's best to play with this extra experience in long sessions versus here and there.
Note: VIP seems to stack with Double XP tickets. The math is quite difficult because of the bonuses and all the numbers going around on the screen. I have came up with a 3.73 times experience when stacking both VIP and Double XP tickets. This is not a confirmed amount, but what I came up with after looking at my stats after a game.
10 Matches - 80 MSP
50 Matches - 320 MSP
100 Matches - 560 MSP
200 Matches - 800 MSP