Basically to earn this achievement you need to fill in two of the silhouettes on the mission select screen. It can be any two including co-op counting as one and you don't need to use the same two characters on every level.
I would suggest playing through on co-op with a friend so you unlock all the powerful weapons and perks then play through as the Sternguard Veteran with a missile launcher, then special power charge +25% and pickup duration +25% perks. Use your special ability often and it should recharge quickly.
Playing as Sternguard Veteran allows you to keep the worst of it at well away from you and dodge most projectiles. I completed the whole game without dieing with this technique. Good luck!