Dark Knight

"The pious Ishgardian clergy guide the flock, and the devout knights protect the weak. Yet even the holiest of men succumb to the darkest of temptations.
None dare to administer justice to these sacrosanct elite residing outside the reach of the law. Who, then, defends the feeble from the transgressions of those meant to guide and protect them?
A valiant few take up arms to defend the downtrodden, and not even the holy priests and knights can escape their judgment. Pariahs in their own land, they are known by many as “dark knights.”
These sentinels bear no shields declaring their allegiance. Instead, their greatswords act as beacons to guide the meek through darkness." — Game Description

Dark Knight, first officially announced during the 2014 London Fan Festival, is a Tank job that wields a Greatsword (2-handed sword) as its weapon. It wields not only a weapon but also the power of Darkness (magic-based tank). Unlike 2.0 jobs, Dark Knight will not have a base class and starts from level 30. It will come with the first expansion pack Heavensward in June 2015.

Unlike other tanks, Dark Knight will use MP instead of TP as its main resource. DK uses MP to cast a darkness buff that drapes the player with a darkness aura. Play style revolves around maintaining the aura, using it for defense, to buff yourself, or offense, to damage your enemies. It is a new style of tanking that will utilize Piety.

Requirements

Heavensward
Access to Ishgard, where Dark Knight's Guild is located.
Complete the quest Our End.

Actions

Details of some of Dark Knight's abilities were announced during the Letter from the Producer LIVE Part XXI:

Grit

This stance will be used when in the tank role. With this stance, it'll be easier to gain enmity, but the damage dealt is reduced.

Darkside

Similar to a paladin's Sword Oath, this stance is more of an attack-based stance. You take on an aura-like effect known as Darkside, while this is in effect your MP will deplete gradually. While in this stance, you will not be able to receive MP healing support from party members. There are weapon skills which restores MP so it’ll be very important to make good use of those skills to manage MP. Darkside can be activated while in Grit stance.

Dark Arts

A buff, similar to Darkside, that drastically increases MP depletion, but allows for more powerful skills to be used while MP is available.

Living Dead

Similar to Holmgang, if the dark knight dies while the action is active, they will enter a zombie-like state with 1 HP for ten seconds. If they are healed to full HP within that time, they will be completely revived. If they fail to reach maximum HP while zombified, they die.

Unmade

A ranged action similar to Tomahawk, that fires dark-tinted orbs at the target.

Plunging Cut

Unlike other tank jobs, dark knight has an action where you jump towards the enemy, so it’ll be possible to use this first then follow-up with an area attack to gain enmity.

Salt the Earth

An Area of Effect spell that creates a Damage over Time field wherever the dark knight chooses.

"Marked for Death"

The dark knight casts this on an ally. If that ally happens to die while the action is still active, the dark knight will receive 20% of their HP and MP back.