Level 59

Total Experience Required 1,113,834 [confirmed]

Level 100 progress: 16.32%

This is roughly:
Killing 3,713 people in Warzone, or...
Killing 3,789 people in Execution, or...
Killing 3,147 people in Wingman, or...
Scoring 795,596 points in Guardian, or...
Scoring 2,421,379 points in Annex, or...
Scoring 1,465,572 points in Submission.

Horde (TU4)

Completing 5,570 waves on Casual, or...
Completing 3,713 waves on Normal, or...
Completing 2,785 waves on Hardcore, or...
Completing 2,228 waves on Insane.

Or a combination of the above. Have fun!