Tall and slender with long black hair, she had a practical mindset and a strong personality defined by an aura of "absolute authority, confidence and credibility". She was a collector of numerous works of art and antique weapons, and favored the perfume Epiphany.
Katherine Mengsk was a patron of charities, including numerous health organizations to aid war victims. She routinely spoke out against interplanetary child trafficking and the plight of Styrling's homeless. She was courted by Angus Mengsk, who she asked to marry her, though he insisted he maneuvered her to ask. Together they had two children, Arcturus and Dorothy Mengsk. When Arcturus was four years old she told him he would become a great leader. Over time Arcturus stopped believing this but she continued to encourage this facet of his personality.
Angus Mengsk's plans for the Rebellion of Korhal put Katherine and the family's life in danger on more than one occasion. In 2478, while Angus planned a secret alliance with Umojan ambassador Ailin Pasteur, neurally resocialized Confederate marines, disguised as a corporate death squad, broke into and rampaged through the Mengsk summer residence. The Mengsk security team took heavy casualties. Katherine took the pistol of the injured head of security, Achton Feld, and killed one of the attackers threatening her son. When the fighting calmed down she treated Feld's wounds.
Katherine walked alongside her husband to the Close of Session event at the Palatine Forum, going against Feld's previous security arrangements. The mood was dampened when Arcturus informed her that he had enlisted in the Confederate Marine Corps, telling her this in front of the entire Senate. She was dismayed When it became apparent her son was not playing a cruel joke, and was even more distressed when Arcturus announced he was departing for training within the day. He left her with the task of delivering his best wishes to his sister as he had not the time to do it himself.
Over the next eighteen months, Katherine eventually came to answer Arcturus' letters, though her messages were far less empathic than the ones she had written to him while he was at the Styrling Academy. Eventually she was reunited with her son when Arcturus returned to Korhal with the rank of lieutenant, though they parted on bad terms.