During the game, you can not only recruit new party members, but also recruit agents. These are NPCs that thanks to a conversation, or a completed quest, decide to join the Inquisition and start working for it. The most notable effects of this are shorter times necessary to complete an operation in the war room, in the Inquisition's HQ. It becomes more pronounced later into the game, because an operation may then take several tens of minutes less or, in extreme cases several hours. Apart from that, recruiting an agent may involve moving the NPC into the Inquisition's HQ (new dialogue options) or gaining access to completely new operations.
The below table presents all of the agents that you can convince to work for you. Some of them are connected with side quests and to learn more, see the walkthrough for the game.
While competing the "Still waters" side quest, you need to reach the place, where Jana is being attacked by the undead. After you get rid of them, talk to Jana and select the special dialogue option that appears on the list, if Solas is traveling with the party.
At the Emerald Graves, you need to complete all activities connected with the " Fairbanks' Trust" quest. Meet Fairbanks at the end and offer him to work for you.
Emprise du Lion
You need to complete "They Call Me Ishmael" side quest and decide to fight the battle, during the quest. After the battle ends, you receive the option to recruit him.
You need to gain the trust of Loranil, who is staying at the dalish elf encampment. You do that by completing side quests that you receive from the elves. Sooner or later, you get the opportunity to recruit Loranil.
Fallow Mire The Fallow Mire
You need to complete the "Lost Souls" side quest. After you win the battle and free the captives, try to exit the fort and you encounter the Avvar. Allow him to become the agent of the Inquisition.
You can recruit the chef after you get the opportunity to try him, during the "Participate the trial" side quest. You need to decide to arm the chief and expel him.
You can recruit this NPC only if you have picked the "In Hushed Whispers" main quest, connected with the mages. Later into the game, you get an option to try Alexius, during the "Participate the trial" quest. You need to allow Alexius to work for the mages, under scrutiny. This is available only if you have the Arcane Knowledge perk.
You need to find her in the tavern in Redcliffe, in the Northern Hinterlands. Talk to Clemence and offer him a job.
To recruit Vale, you need to complete six side missions in Hinterlands - "Hunger Pangs", "Apostates in Witchwood", "Templars to the West", "East Road Bandits", "Healing Hand" and "In the Elements". You can then meet Vale at the crossroads in the center of the map. Pick the dialogue option to recruit him.
You need to complete the "My Lover's Phylactery" side quest, i.e. supply Ellandra with the phylactery that you find in Hinterlands. During the final meeting with Ellandra, ask Vivienne to take part in the conversation (she must be on the party) or select the special dialogue option, which I available after you have chosen the Arcane Knowledge perk.
Go to the southern citadel in Hinterlands. Complete a part of the "Praise the Herald of Andraste" side quest, thanks to which you can infiltrate the citadel. Find Lord Berand here and recruit him.
You need to take quite a few steps to recruit Dennet. Start by completing four of his side quests, connected with the Hinterland farm - "Horses for the Inquisition", "Master of Horses", "Trouble with wolves" and "farmland Security". Finally, meet with Dennet. You can ask him to join the Inquisition in two ways - ask Cassandra to help you (she needs to be on the party) or pick the special dialogue option, unlocked by the History Knowledge perk.
You need to complete the "Praise Herald of Andraste" side quest in the Southern citadel, in Hinterlands. During the final conversation with Anais, convince her to take the position of the Inquisition's spy (an appropriate dialogue option).
You need to complete the "Strange Bedfellows" side quest and during the final conversation with Ritts, pock the special dialogue option that appears only if you have Varric on the party.
You need to complete the "Business Arrangements" side quest. During the final conversation with Sister Tanner, pick the dialogue option that appears only if you have Cassandra on the team.
The Storm Coast
You need to complete the "House Clearing" side quest. It is VERY important that you do not skip the preparation and wearing the Mercy's Crest. This will allow you to fight a honorary duel against the bandit leader, towards the end of the quest. After the battle, wait for the conversation with one of the regular bandits to start (Hessarian Blades).
The Western Approach
You need to do a lot of things to recruit Frederic. Start by completing the five side quests in the Western Approach- "Frederic's Livelihood", "Draconology", "How to Lure a Dragon", "Hunting Patterns" and "Sharper White Fangs". Additionally, you need to defeat the High Dragon in this location. Finally, meet with Frederic again and invite him to the Skyhold.
The Western Approach
You need to do a lot of things to recruit Servis. Start with completing the "The Trouble With Darkspawns" side quest, in the Western Approach. Then, towards the end of the mission, pick the option to capture Servis alive. You then need to wait until there appears an option to try Servis. Make him a spy or a smuggler for the Inquisition.
The Winter Palace
During the "Wicked Eyes Wicked Hearts" main quest, you need to win against Florianne. You get to recruit the agent, regardless of whether you captured or killed her. In both cases, you need to wait for Florianne's trail to become available in the Skyhold - the "Participate the Trial" quest.
The Winter Palace
During the "Wicked Eyes Wicked Hearts" main quest, you need to talk to one of the mercenaries in the main yard and recruit him. This becomes possible if you pick the special dialogue option that is made available by the Underworld Knowledge Inquisition perk.
You can recruit him only if you chose "Champions of the Just" main quest, connected with Templars. During the quest, make sure that Barris survives (do not leave him for too long in the huge chamber). You gain access to the option to recruit Barris after you win the battle against the Pride demon.
During your first visit to Val Royeaux, you need to find her (the "Threat Remains" main quest) and talk to her.