The Grand Coven is the supreme command of all witchcraft. Without their sanction, I’m forbidden to practice!
The Grand Coven was the supreme command of witches, sanctioning witches in their use of magic. According to the Grand Coven there are three types of witches in the world, the first and most common are the "borrowers" -- witches that get their power from demons, presumably in exchange for their souls. The second type, and rarest are the "naturals" those born with a natural ability for magic. Thirdly are the "students" who are trained and mentored by Grand Coven approved witches.
The Grand Coven's power has become severely reduced to the brink of being decimated by the Men of Letters; who used their political influence to whip the church and public into a frenzy over witchcraft, and taking advantage by plundering their archives of spells and potions and storing them in their bunkers all over the world.
- Olivette: The High Priestess of the Grand Coven, Olivette is a British witch who was responsible for uncovering Rowena's past and sending her on the run from the Coven. She was captured by Crowley and brought to Rowena who tortured for information on the Coven's plunder of potions and spells. After realizing how the Men of Letters brought the Coven to the brink of decimation, Rowena attempted to kill her, but she changes her mind and transforms her into a hamster. She is currently kept in a cage in the Needham Asylum.
- Rowena MacLeod: A Scottish natural born witch, Rowena was initiated into the Grand Coven, overlooking her past of marrying a non-magic person and giving birth to a son; Fergus, because of her talent. Her magic, which results in boiling people's brains, was declared too extreme, resulting in her formal separation from the Grand Coven who forbade her from using magic and cast a binding spell that limited her magical abilities.
- Katja: A German witch who inspired the Brothers Grimm to write the famous story; Hansel and Gretel. She and Hansel were sent to locate and kill Rowena, and all the while turning people who wouldn't be missed into children, fattening them, and cooking and feasting on them. She was killed by Dean Winchester who locked and burned her alive in her furnace, which was how the witch was killed in the story.
- Nadya: A Grand Coven witch which was highly skilled at deciphering complicated codes and using them to encode her codex which contains her decryption formulas. She was killed by the Men of Letters and her codex was stolen and hidden at St. Louis, Missouri in the Werther Box by Cuthbert Sinclair in 1956 and it remained there until it was recovered by Sam and Dean in 2015. Sam then took the codex to Rowena with the hopes of decrypting the Book of the Damned to find a cure for the Mark of Cain.
Rowena mentions how the Grand Coven cast her out and has prevented her from actively practicing magic.
Rowena begs Crowley to make a case to the Grand Coven, which she describes as the supreme command for all witches for her to practice magic freely again. Eventually he captures High Priestess Olivette for her to do as she will. Under torture, Olivette reveals that the Coven has been decimated and is "a pale relic of its past power." The Men of Letters used their political power to whip the church into a frenzy and many of the best members of the Coven were burned at the stake or forced into hiding. The Men of Letters then plundered their most powerful spells and potions and scattered them through warded bunkers across the world and in their weakened state the Coven wasn't able to get them back. Rowena loses her fear of the Coven and turns Olivette into a hamster and decides to search for the missing spells and potions for herself.
Rowena reveals that a Grand Coven witch named Nadya was murdered by the Men of Letters who took her codex that could decode the Book of the Damned. Sam begins a search for the codex, eventually finding it in the Werther Box.
With the Book of the Damned and Nadya's Codex in her possession, Rowena begins recruiting Grand Coven members to join her "Mega Coven." The first group, a trio of witches scoffs at her idea, believing she is merely looking for protection from the Winchesters and the rest of her multiple enemies. Rowena noted that what remains of the Grand Coven has become obsolete and beginning to crumble ever since Olivette's disappearance, which the witches know that Rowena had a hand in. They pass her off as being more delusional than ever, but for their rejection of her offer, Rowena performs an incineration spell that burns the trio into ashes from the inside out.
Next she meets with a duo in a restaurant, who are more receptive to her offer to join her Mega Coven. However, a demon assassin sent by Crowley interrupts, killing one of the witches as Rowena flees. Sam and Dean later meet with the surviving witch, who refused to leave the police station out of fear, and have her cast a scrying spell to locate Rowena.
Rowena reveals to Sam and Dean that before she was exiled, the Grand Coven cast a binding spell on her to limit her powers, but she believes that the Black Grimoire has a spell that can reverse their hex and unlock her full potential with the hope that she can use the extra power to protect herself from Lucifer if he tries to kill her, again.
After killing the Plum Sisters, Sam gives her the page that contains the spell. Rowena is later seen in a hotel room casting the spell on herself to lift the Grand Coven's bindings.