Anne Finnelan is a teacher at the Luna Nova Magical Academy, where she serves as an instructor in subjects including Magic Linguistics, History of Magic, and Object Control Magic, in addition to handling student counseling and academic affairs. She is a middle-aged woman with brown hair typically styled in a bun with two front strands, blue eyes, and a pale complexion, and she wears the standard Luna Nova teacher uniform with a hat adorned by two feathers.

Finnelan is a serious and authoritative figure who demands respect and discipline from her students. She is generally calm but quickly loses her temper, particularly when dealing with incompetent students or troublemakers. She holds a deep respect for the most formal style of witchcraft and is deeply committed to preserving the traditions and prestige of Luna Nova Academy, believing that all witches should be formal, collected, and act serious at all times. This dedication makes her rigid and unwilling to compromise when crises threaten the academy, especially if available solutions would affect its traditions or reputation. She has a clear preference for magically gifted students like Diana Cavendish, often treating them with kindness, while holding prejudice against those who lack magical talent or favor a technological approach to magic.

Her motivations center on upholding the rules and standards of Luna Nova at all costs. She is disgusted by bad manners, rule-breaking, and what she perceives as undignified behavior from both students and fellow faculty members. This leads her to frequently clash with Atsuko Kagari Akko, whose clumsiness and unconventional methods she views as a disgrace to the academy. Finnelan does not hesitate to suggest expulsion for students she considers hopeless, though her harshness stems more from a desire to maintain institutional standards than from personal dislike. She also shows disdain for Professor Ursula, whom she considers careless and too lenient, often reprimanding her for her demeanor and perceived lack of proper guidance for students. Her suspicion of Croix Meridies and her magitronic innovations proves justified, as Finnelan remains opposed to mixing magic with modern machinery while other faculty are won over, and Croix later reveals hidden motives that endanger the academy.

In the story, Finnelan plays the role of a strict authority figure who enforces discipline and represents the traditional values of Luna Nova. She appears in numerous episodes, from the opening ceremony where she is surprised by Akko sudden appearance, to teaching the Lunar Alphabet in her Magic Linguistics class where only Diana proves able to understand it. She punishes Akko and her friends for various infractions, including stealing tarts from the kitchen, creating a monster mushroom during a potion class, and escaping detention to attend a book launch event. During the crisis with the dragon Fafnir, she struggles to translate an ancient contract until Diana intervenes, revealing that Fafnir had been scamming the academy for years. When Croix proposes her Sorcery Solution System to resolve a strike by fairy laborers, Finnelan firmly rejects the offer before begrudgingly accepting when the situation escalates. She later confronts Croix directly about the magical anomaly surrounding the Noir Rod, only to be rendered powerless when Croix shuts down the Ley Lines around Luna Nova.

Her key relationships define much of her role in the series. With Akko Kagari, she shares a relationship of mutual frustration, as Finnelan cannot see value in Akko clumsy efforts while Akko continues to defy expectations through sheer determination. Ursula points out that Finnelan preference for competent students blinds her to genuine determination and effort, and that her disdain has gone too far. With Diana Cavendish, she shares mutual respect and admiration, frequently praising Diana magical prowess and maturity, though her complete confidence in Diana leads her to erroneously credit Diana with restoring the Jennifer Memorial Tree when it was actually Akko work. With Ursula, she shares a relationship of professional criticism, often reprimanding her colleague for her clumsiness and lack of proper authority, though Ursula stands up to her to defend Akko. With Croix Meridies, she maintains consistent opposition, as Finnelan is the most vocal opponent of bringing modern machinery to the school, and her suspicions are later validated when Croix plans are exposed.

Anne Finnelan undergoes notable development throughout the series. While initially unable to see any value in untalented students, she gradually begins to recognize determination and effort. In the manga adaptation by Keisuke Satō, after the events of Orange Submariner, she learns not to let her personal perspective cloud her judgment, taking time to investigate a situation thoroughly rather than shouting accusations, and she is impressed by Amanda ONeill maturity in confessing to wrongdoing. When she witnesses Akko successfully levitate on a broom for the first time using her own power, she is seen smiling with pride, demonstrating that her faith in Akko abilities has improved. By the end of the series, she joins the rest of the academy in giving their energy to Akko and Diana during their final battle, and later celebrates Akko success in finally flying with her broom.

As a witch, Finnelan is highly skilled and experienced, recognized as one of the best teachers at Luna Nova Academy. She demonstrates the ability to cast the advanced and complicated Luna Lana spell, which she uses in combination with Diana to destroy a giant monster mushroom created by Akko and her friends. She can create sturdy magical barriers, has great ability in object control magic sufficient to teach it at the academy, and like other teachers, can project images and scenes in thin air. As the Magic Linguistics teacher, she possesses deep knowledge of many magical languages, including the ancient Luna Alphabet.