The Head Privateer Office is located on Isle Fortuna. It is two stories, and has several offices.
The Head Privateer Office is at the top hill of Isle Fortuna, overlooking the docks, and the marketplace.
The layout of the building is similar to the Armory Office on Kingshead, except that you can enter. There are two entrances: the main door, which is guarded by two EITC thugs (non-hostile), and the second story door, which is accessed by a small staircase.
If you head through the front door, you will be in the foyer. The foyer is a loft, with several doors. On the left of the foyer, ae two small offices, which are both occupied by a non-hostile Royal Navy NPC.
If you walked straight forward, you would come to a door marked "Cellar". Entering the cellar will bring you to a large cellar, with many shelves. In the far corner of the cellar is a man flipping a coin, who is named Quartermaster Reilly. He stands near a locked trapdoor. (Note: it will be unlocked for a certain time in one quest.) Going into the trapdoor, you enter a dirt tunnel. As it has been carved out, there are beams holding it up. Directly across from the entrance is a makeshift door. Entering the makeshift door is another tunnel. At the end of that is a elevator going down to Fortuna Caverns.
Back in the foyer, if you take a right, you will walk onto a staircase. Following the staircase, you will be brought to the upper floor of the loft. Straight in front of you is a portrait of Admiral Pistol. There will be a short hallway, stretching to your left, and to your right.
Going to your right, you will see a door. Go through that door, and you will have discovered the back entrance. Follow the hallway to the left, and there are a few rooms. The first room on your left is the office of Quartermaster Reilly. The first room on your right is just a small office for an EITC non-hostile NPC. The next door on your left is Admiral Henry's office. The end of the hallway is a small table with a vase on it, and a portrait of King George II above it.
Entering Admiral Pistol's office, you will enter a hallway. At the end of the hallway is a highly-decorated square room. In the center of the room is a large mahogany desk, where Admiral Pistol can be seen doing paperwork. There are many bookcases and mounted weapons in the room. Behind Admiral Pistol is a grand fireplace.