How do I become a vampire? (in ESO) [duplicate]

There's no specific "vampire guild" in the game. Also there's no minimal level, although the process of becoming a vampire or werewolf is easier with higher levels (you'll have to complete a quest line which will somewhat scale to your level).

The basic idea is, that you've got two possibilities to become a vampire (or werewolf) in the game:

• Get infected by a NPC vampire or werewolf. These have to be from special encounters you'll find in the highest level zone of your home alliance.

• Get infected by a player vampire or werewolf. Players who are already a vampire or werewolf can buy a passive ability, which allows them to infect other players once every 7 days (real-time). This is only possible at special, hidden shrines, once again found in the highest level zone of your home alliance.

The highest level zones for the different alliances:

• Aldmeri Dominion: Reaper's Mark
• Daggerfall Covenant: Bangkorai
• Ebonheart Pact: The Rift

It is not possible to become a vampire or werewolf by being attacked by random werewolf or vampire NPCs nor is it possible to get infected by being attacked or killed by a vampire or werewolf in PvP.

As mentioned, there's no specific guild to join. However, there are some guilds in the game that do either role-play vampire clans or werewolf packs (who'll initiate you sooner or later), but there are also guilds just existing to find/sell someone the "gift" of becoming a werewolf or vampire.

Just keep in mind that players can pass this for free, so any payment is really just a thank-you. Many will ask gold for this, but there are also many who'll happily pass the skills onto you for free. Just keep your eyes open.