The birth and early life of Karnilla were shrouded in mystery. All that was really known of her early past is that she had lived in Nornheim, the Asgardian province where the Three Norns dwelt. They were the goddesses of destiny, and Karnilla became one of the most accomplished practitioners in the arts of sorcery within the Asgardian dimension. Although, Nornheim sat on the Asgardian land mass within Asgard's own dimension, and Karnilla was apparently of the Asgardian race, she did not consider herself to be subject to Asgardian rule. Nornheim was an independent country, of which Karnilla was absolute Monarch.
Karnilla lived opulently in the ancient fastness of Nornkeep, attended by her servant, the aged minor sorceress Haag, and troops of guardian demons. Although there were many demons among her subjects, Karnilla's realm was also populated by humanoid immortals, just as was Asgard proper. Karnilla's relationship to the goddesses of destiny was unknown, although they were clearly beyond her jurisdiction.
In the past Karnilla often proved to be an enemy of Asgard, and acted in alliance with the Asgardian god of evil, Loki. However, Karnilla was long in love with Asgard's noblest warrior, Balder the Brave. On Balder's request (on behalf of Asgard's monarch Odin), Karnilla allied herself and her army with Asgard in the war with Surtur. After years of resisting Karnilla's advances, Balder finally became Karnilla's lover. Some of Balder's Asgardian friends disapproved of the relationship, regarding Karnilla as a figure of evil. Karnilla regarded herself, however, as a harsh but just ruler.
Balder was called away from Nornkeep to join the Asgardian prince Thor in his mission to rescue souls of Earth human beings from Hel. During Balder's absence, Karnilla was taken prisoner by the Frost Giants of Jotunheim, who were preparing an invasion of Asgard and first intended to eliminate Asgard's allies. The Frost Giants also transformed Karnilla's subjects into stone. On his return, Balder set out to rescue Karnilla, and ultimately met with success.
Her present activities are unknown at this time.