You unlock this achievement by completing all three of the Resistance Ring covert actions called "Hunt the Chosen" Part 1 and Part 2 ("Hunt the Chosen Assassin", "Hunt the Chosen Hunter", and "Hunt the Chosen Warlock").
The order of events by which the Part 1 covert actions become available depends on whether you had the War of the Chosen Introduction selected during your game setup. The long and short of it is, you have to make contact with all three factions and you have to make contact with one of the Resistance regions claimed by each of the Chosen. Note that unlike the other covert actions, these do not expire or cycle in and out, so feel free to wait until you're good and ready before doing them. That being said, completing them brings a nice reward of allowing you to have more Resistance Orders going on simultaneously, so it's good to get them done early on, if you can.
The Part 1 actions require a sergeant or higher, a second soldier of any rank, and an optional third soldier to negate the risk of an ambush. Completing each Part 1 action raises your influence with one of the Resistance factions to Medium.
Each Part 2 action immediately becomes available upon completion of its corresponding Part 1 action. They require a lieutenant or higher, a second soldier of any rank, and an optional third soldier of sergeant or higher to negate the risk of capture. As you complete each Part 2 action, your influence with one of the factions goes to High. Complete the third Part 2 action, and the achievement will unlock.