Under New Management

This is, overall, the final quest in the Thieves Guild for Skyrim, as it is where you assume the role and title of the Guild Master. It requires you to have done all 'special' city jobs from Delvin Mallory and Vex (not including Larceny Targets) and the entire chain of main quests. However, keep in mind that, special jobs are offered by Delvin only after five 'smaller' jobs have been completed in Whiterun, Markarth, Windhelm and Solitude, respectively, to restore the Thieves Guild's influence in that city. Review the Small Jobs and City Influence Quests sections for details as well as Conditions and Tips.

Once these are complete, speak to Brynjolf who is wandering around between The Ragged Flagon and the Cistern and follow him to the center of the Cistern where the Guild officers will initiate you as the new Guild Master.

Rewards

 * Guild Master's Armor Set (35% pickpocket, 35% lockpick, 50 points carry capacity, 20% better prices)
 * Amulet of Articulation (persuasion attempts almost always succeed, speech is 5-35% better)
 * Key to the Guild's Tribute Chest (Chest located in front of the Guild Master's Desk in the Cistern that gives random loot, gems, coins, enchanted weapons, etc.)
 * Unlock the achievement : One with the Shadows.