As one of the most powerful younger wizards of the White Council, Harry has a large repertoire of magical powers. His skills at evocation, or ‘quick and dirty’ magic, aka "kaboom magic", aka "battle magic", lean toward large blasts of fire and force, sometimes using wind, and also has some skill with earth (usually manipulating gravity) and lightning magic. He has considerable magical brute strength, though his control is initially somewhat lacking - for example, while he could easily shatter a pair of handcuffs, he may also break the wrists of the person wearing them. For this reason, Harry is ofttimes referred to as a magical 'thug'. Later in the series, Harry is also shown to have tremendous power in ritual form battle magic, when he uses the energy of a ley line to concentrate gravity for several miles around into a small zone, and flattens hundreds of enemy combatants at once.
Harry's skill with battle magic has increased steadily and quickly. His shields are the most striking example, initially unable to deal with sufficiently strong attacks, and not warding away heat, such that his hand was almost burned off. Now, thanks to practice and improved foci, they can deal with significant attacks without a problem. While the head of the Wardens has sufficient focus to wield fire magic with a pinpoint laser-like effect that can cut a person in two, Harry has the power to take out a building, fry an I-beam, and has 'upgraded' to a blue-white shot of fire magic strong enough to bore through a Denarian. Harry is also using physics more, using his shields to turn enemies attacks back upon themselves or their allies, and ripping heat away from areas to create ice as well as power fire attacks simultaneously, and transforming himself (and a White Court vampire) into an explosion-powered cannonball.
Harry was frequently accused of a lack of subtlety in his magic until he began training Molly as his apprentice. Through teaching to her particular talents (especially for veiling) and weaknesses (concentration, less emphasis on violent magic), Harry gained a greater understanding and finer control over his talents and began using subtler versions of his own spells, such as tightly controlled wind gusts. Changes shows Harry developing the following: much better control (he starts using illusions, veils, and Luccio's cutting fire beam, raising and lowering shields with great speed; and fine uses of soulfire), huge area effect spells; pure mental summoning of extremely powerful entities without a summoning circle; and using the fire and ice exchange trick in combat multiple times.
During the events of the novel Changes, Harry takes up the mantle of the Winter Knight. It is a position of incredible power, giving Harry access to the abilities of the Winter Sidhe, though ironically, he still complains of his aversion to cold, something the position failed to take away. This gives him substantially more stamina, speed, and strength in both the physical and magical sense, improved ability with "ice magic" which he either lacked or was reluctant to use prior to his appointment, and give him greater protection from physical attacks. It is presumed that Harry will hold the mantle of Winter Knight until he dies, as only with the death of the old knight can a new one be named (though Jim Butcher has stated that Harry is still the Winter Knight in the novel Ghost Story).
Harry was able to employ Hellfire while possessed by the Shadow of the Denarian Lasciel, a power that especially aided destructive spells and fire effects. After Harry lost that power, the Archangel Uriel awarded him the Angelic power of soulfire, which is used to make a sort of magical framework for the magic being used, turning, for instance, a straight force attack into an enduring silvery construct hand able to bash and batter repeatedly. The portion of the soul used in the soulfire returns over a period of days, enabling the wielder to get back to full strength; using all of one's soul is still fatal, however. Soulfire excels when used in creation magic, a notable example of which is illusions.
Magic itself has an innate power to disrupt technology in the Dresdenverse. A strong wizard's aura interferes with devices such as computers, airplane engines, and car motors, severely limiting his use of any modern/electronic gadgets. ("I can kill a copier at fifty paces," Harry remarks in Storm Front.) As a result, Harry becomes a potential safety risk whenever he visits places containing sophisticated equipment, such as hospitals in which patients are on life support. He prefers older, less refined technology when he has to deal with it; he drives a 1960s Volkswagen Beetle, knows a mechanic who can keep it running eight or nine days out of every ten, and favors revolvers over semi automatic pistols when he needs to carry a firearm. Harry uses candles, a fireplace, a kerosene heater, and an icebox in his apartment and lab, and he keeps dozens of spare light bulbs in his office in case one burns out when he walks past it. He can deliberately cause widespread havoc around high-tech items just by drawing in his magic, a practice he refers to as "hexing."
Because of this technological stricture, many wizards employ the Nevernever to travel long distances. If a wizard knows the path, they can step into the Nevernever, walk a short distance, and emerge somewhere else far away, as distance and time function differently inside. Due to their difficulty in using advanced means of transportation, control of paths and locations in the Nevernever is of critical importance to wizards for getting around rapidly. Knowledge of access points to the Nevernever is among the more useful secrets in the Dresdenverse...and an important bargaining chip for the Faerie Courts, who control most of the Paths through them. Dresden's mother was one of the most knowledgeable of such travelers. According to Luccio she would breakfast in Prague, lunch in Rome, and be in Tibet by sundown, with a couple of stops for coffee along the way. Harry obtained a red crystal belonging to his mother in Changes, which contains his mother's knowledge of these paths, which vastly outweighs his own. He has become slowly better, faster, and neater about opening portals to the Nevernever…he even uses one as a shield in combat to absorb falling stalactites from a collapsing ceiling.
Harry also possesses great skill at thaumaturgy - he prefers it, since it gives him more structure and precision for his power. According to Harry, his skills lie in "redirecting energy, sending energy out into the world to resonate..." in White Night. He is particularly well-versed in spells that track and find others. Harry has summoned spirits across multiple mythos in his time, including faeries big and small, Voodoo loa spirits of knowledge, and actual demons, using this skill and thaumaturgic rituals. His first use of a ritual in battle is in Changes.
A power that all true wizards have is The Sight, or the Third Eye. Using this power is one of the earmarks of wizardry. It allows a wizard to see the world as it truly is, on a magical and spiritual level, bypassing all veils and illusions and showing people and things as they truly are. Anything that is witnessed under the Third Eye is remembered perfectly, forever, which leads to reluctance to employ it, as it is often called on in situations to reveal evil, horrible supernatural harm, and the like, and the weight of such memories can cause significant mental stress over time. Harry's first use of the Sight was on a tree, and he can perfectly picture the gnome-like spirit within it to this day. His use of Sight on the Skinwalker (in Turn Coat) nearly drove him mad with fear and terror at the depth of the evil, cruelty and anathema he witnessed within the creature. It is noteworthy he has never used True Sight on a true Denarian, although he has witnessed the conflict of the Fey Courts using this ability...which completely turned his estimation of the power of Mab on its ear in his awe (and fear). (In Book One of the Dresden Files, the 'drug' being manufactured by the antagonist is actually an alchemical potion allowing normal mortals to use True Sight, an experience few are ready for.)
Yet another power that all wizards have is the soulgaze, a meeting of the eyes that transforms into a highly personalized and revealing look at the other person's psyche and soul, and one of the reasons why people instinctively don't look deep into another's eyes. It is an immediate way to identify someone or something flawlessly. It is notably something he has never shared with Murphy, although he has with Susan. Harry has no idea how people perceive him, although those who have Gazed him tend to have their opinion and respect for him taken up several notches after it happens, as they realize the true nature of who they are dealing with. The crime lord Marcone, for instance, evidences a remarkable amount of respect for Harry after sharing a soulgaze, and a young wizard who shared a soulgaze with him said that Harry was gentle, kind, and alone. However, in the few instances when Harry has Gazed an enemy during a confrontation, they generally have had a horrified reaction (one even gasped that he "[didn't] believe in hell").
On a more mundane level, wizards like Harry are also capable of slowly 'healing perfectly' from injuries, leaving no scars or breaks. For example, his broken bones will seal and leave no mark behind, and he is slowly regaining use of his flame-seared left hand, damaged so severely the normal doctors recommended it to be amputated. This characteristic is the probable reason for the exceptionally long lifespan of wizards. It has limits...a wizard might take 40–50 years to heal the broken back Harry suffers in Changes. Luckily for him, his back problem was fixed instantly when he became the Winter Knight.
Harry's 'final' ability possessed by all wizards is that of the death curse. While it is typically targeted at the being that kills them, it may be employed upon anyone within line of sight (such as when Harry was readying to send the Death Curse at one of the Necromancers in Dead Beat when he anticipated Morgan's attack), and the wizard must have time to use it (a few seconds). Death curses can be incredibly powerful. Harry believes that the force of his curse could wipe every living thing off the island of Demonreach, and others agree. His mother's Curse completely blocked the ability of the King of the White Court of Vampires to feed, a creature that was otherwise immune to magic. He himself has been the target of a Death Curse, although the lesser power of the caster left it open-ended and of vague purpose.
Starting with his first exposure to the island of Demonreach, it also appears that Harry is starting to develop foresight, a characteristic seemingly common to all wizards as they get older (and are not warned about ahead of time to stop them from wondering if this or that event was foreseen).
Additionally, after bonding with the native spirit of Demonreach in Turn Coat, Harry is able to link in with the spirit's intellectus ability concerning itself and all upon the island, enabling him perfect knowledge of Demonreach and its denizens, and natural harmony with the creatures dwelling there, giving Harry an incredible tactical advantage while he is present.
It seems that by the timing of Harry's conception and birth, he has some form of power over Outsiders, such as He Who Walks Behind, resulting in his astonishing ability to overcome a major Outsider while still a teenager after his master had sent it after him, and actually surviving an Entropy Curse (a lethally malevolent form of bad luck).
Harry has a fairly uncommon magical power he has developed with time and experience, the ability to Listen. This is more akin to a clairvoyance effect of limited range than merely enhanced hearing, but the sensitivity of it has risen with time, to the point where Harry can even filter out and discern different heartbeats around corners and in rooms close by. Although it can be stopped by a Veil, it provides an excellent tactical edge against many opponents for him.
Unlike some of the other magic users in the series, Harry shouts faux Latin commands to perform spells. For example, Harry lights candles in his apartment by muttering "Fliccum Biccus," an allusion to the "Flick your Bic" lighter advertising campaign. When Harry utters this phrase and infuses the spell with a minor effort of his will, his candles light up or the fire in his fireplace comes to life. He explained that most magic users use some language they're not familiar with for their incantations, to provide a bit of magical insulation to the user's mind from the forces they are channeling and avoid accidentally casting a spell by uttering a common phrase in a language they're used to. His ex-lover Elaine uses Egyptian.
Ghost Story drops Harry into the life of being a spirit/ghost, and a whole new set of magic. We learn that ghosts can 'vanish', like a short-range teleport, they hurt one another with strong memories, can consume other ghosts for their memories, are destroyed if caught outside a sanctum by the morning light, and can wield magic once again by calling up memories of having used magic before. However, casting magic is fueled by the essence of the spirit itself, much like soulfire, and can consume them entirely if not watched for. Ghosts can manifest physically by use of extreme willpower, as well.
Ghost Story also introduces us to the mechanics of mental assault and defense in the Dresdenverse, the uses of advanced illusionary ability via Molly Carpenter's burgeoning ability, and the rather spookily powerful abilities of ectomancers, the people who can speak with and control ghosts (a very separate line of study from necromancy). Harry's mental ability is noted as being incredibly obdurate on defense, and blundering tough on offense. Molly is noted as being swarmingly effective on offense and elusive and hard to find on defense.