To reach rank 30, you need 423,700 XP.
This is the longest achievement in the game, and reaching rank 30 will take an extremely long time. The game generally doesn't reward average players well, and even higher performing players will still only gain a small amount of XP compared to how long it takes to rank up between levels. Overall, co-op missions, more specifically the Hardcore tier, will be the quickest way to level up. You can also purchase XP boosters from the store with real money to make levelling up substantially quicker. Assuming you consistently play and complete Hardcore missions without using boosters, a rough estimate for this achievement is 60+ hours.