Born into the prestigious and mysterious Hellsing family, Integra has been sheltered and educated all her life to take the place of her father as Bureau Director of the Hellsing Organization. Integra's Mother does not appear in her flashbacks, suggesting either that Integra never met the woman or that she died when Integra was very young. When she was 12 years old, Integra's father passed away and entrusted her with their family's mission to lead the Royal Protestant Knights and protect England against the vampires.

Immediately after Arthur’s death, Richard Hellsing, jealous of Integra for inheriting the family headship, attempted to hunt her down and kill her. Integra escaped her traitorous uncle and managed to reach a dungeon in the mansion's sublevels, where her father had said she would find her salvation. Hoping to find a knight, she stumbled across an old, dried-out corpse instead. Richard found her, cornered her, and shot her in her shoulder, spilling her blood across the floor of the room. The corpse, who ended up being a vampire whom Arthur had imprisoned 20 years earlier, awoke and licked up Integra's blood. Rejuvenated, it proceeded to kill her persecutors, thus saving her. Richard desperately attempted to kill Integra one last time, but the vampire blocked his bullet. Picking up a gun, Integra shot and killed her uncle, becoming the last descendent of the Hellsing bloodline. The vampire, whose name was Alucard, became her loyal servant.

Not long after, Integra was knighted and introduced to Vice Admiral Sir Shelby Penwood, a former friend of her father. Upon seeing Integra for the first time, Sir Penwood said that she was far too young to fulfill her duty. He revised his opinion during the actual storyline, in which he admitted that it was an honor to have met and served with her in his farewell message, prior to his death. His sacrifice was just one of the many examples that helped solidify Integra's resolution about humanity's worth and continue her duty.

Integra as a child was more timid than she is now, yet a very willful girl, being brought up with a commanding presence that even Alucard respects. When Alucard became her servant, she grew more confident and comfortable with her position as head of the Hellsing family and a Knight of the Round Table. Much like Seras Victoria, Integra experiences a coming of age, gaining experience and losing her remaining innocence as events unfold and the war begins, transforming into a leader with an iron resolution who does not flinch at the first signs of danger and who gains wisdom through dire losses and betrayals. The Major recognizes her change from a "beautiful Fräulein" (he goes so far as to apologize for calling her this) to the most dangerous enemy who stands in the way of his plans, calling her forth into his Zeppelin. Inside, she and Seras slaughter the remaing forces and then approched the Captain, Integra leaves Seras to go fight the Werewolf while she goes for the Major.

When Integra reaches the Major, she attempts to attack him but is stopped by a glass dome. There, she witnessess Alucard's dissapearance when he unknowingly drinks the blood of Schrödinger. After defeating the Captain, Seras arrives and uses her cannon to break the dome. In the process, she ends up blowing off half of the Major, revealing that he is a cyborg. Integra approaches the Major and guns him down, but a shot from the Major hits Integra in the eye. Integra and Seras escape from the giant Zeppelin.

After the thirty year transition, we discover that Integra is still the head of the Hellsing Organization but has accepted the fact that family-run agencies are a thing of the past and that government agencies will someday take over her organization. She and Seras have grown considerably close over the course of thirty years and the two anxiously await for the day when Alucard will return (though Integra has her doubts). In the final chapter, Alucard returns and attempts to bite her, but she shoots him before he has the opportunity. Once she realizes it was him, he explains his thirty year absence and says that he has not had blood in all that time. When Integra reminds him that she is an old woman now, he doesn't seem to mind. She bites her finger enough to draw blood and allows it to drip into his mouth after welcoming him back.