He appears in one mission of the storyline, where he saves Buck from a demon attack while he is fighting Coward Mark across the lake in Oregon. Afterwards, Buck asks where he can get a Witch Impaler. The Exorcist told him that he cannot until he is a member of the Brotherhood. Buck rejects the offer, since he is already on a mission, but he tells the Exorcist that they will probably meet again.
The Exorcist assists Buck in defeating Lone Wolf. He later knocks Buck out and captures him to tell him that his wife is a witch and that the barman is in fact the head of the gang, who wanted his partners eliminated after they abandoned him.
The Exorcist will later die in the storyline when using The Consecrator to kill Buck's wife, and Buck will carry his body away. You later see his grave with his hat on top of it. Buck says "I'll rid the world of evil or die trying" to repay the Exorcist.
In the mission "Fight the Demon", the mission intro says "Go to the Socorro cemetery and help the Stranger fight the powerful Red Witch.". But actually, the Exorcist is nowhere to be seen, so the mission intro is a lie.
In the few missions that he actually fights beside you, he can actually kill you due to the Witch Impaler's splash damage. His taunt after killing you is the same as the Confederate Soldier's taunt.
Despite the fact that the Witch Hunter is a human, his skin color is blue.