Leaving aside the fact that you're essentially wrapping a living being around yourself, it often forms some sort of symbiotic connection with the wearer, often drawing nutrients from the wearer's blood. Needless to say that might have adverse side effects.
Things can be pretty bad for the wearer if this is combined with Clingy Costume, either because the armor doesn't want to let the user go, or because the process of grafting a living armor suit to a human host is irreversible. An even worse version might be sentient, and capable of taking over.
Might be worn by a Heroic Host. Might sometimes be able to turn into an Animated Armor. Subtrope of Organic Technology. Compare Living Weapon, a creature used as a weapon; and Living Clothes, clothing that has a mind of its own, though it may not necessarily be an actual organism in itself.
- Guyver is a classic anime and manga series about a high-school kid who gets his hand on a powerful set of technorganic armor that enhances the capabilities of its host and has to fight monsters called Zoanoids. The armor is virtually indestructible, and is able to regenerate from pretty much any wound, its only weak point being its Control Metal. As long as the Control Metal is intact, it can rebuild the host from the data stored within. But if it's critically damaged, the suit will eat the host alive.
- Jushin Liger. It was even retitled Bio Armor Ryger in the West, although it was more of a bio-Humongous Mecha than a bio-armor.
- Obito Uchiha, having survived being crushed by a massive boulder and rescued by Madara Uchiha, is recuperating at Madara's lair and watched over by White Zetsu and a hollow spiral-faced Zetsu called Tobi. When told that his friends are in danger, he tries to leave to help them but is insufficiently recovered to do so, prompting Tobi to offer to let Obito use him as armor.
- The Version Two state that Jinchūriki can access — wherein the user is covered by an opaque form-fitting "cloak" of reddish-black Beast chakra, giving them Blank White Eyes and a Jagged Mouth — qualifies, given that the Tailed Beasts are Animalistic Abominations made of chakra. In this state the Jinchūriki can also manifest parts of the Tailed Beast's skeleton to act as armor or augment attacks.
- Neon Genesis Evangelion: Much like the aforementioned Jushin Liger, the EVA units are bio-Humongous Mecha with organic parts cloned from aliens.
- Marvel Comics: The symbiotes are amorphous entities — sometimes alien, sometimes not, depending on the continuity — that bond to a host, encasing them in their biomass and acting as a living costume. They provide enhanced strength, durability, and various shapeshifting powers, but often at the cost of becoming a monster. Venom and its offspring Carnage are the most famous examples, though dozens of others — like Toxin and Anti-Venom —have popped up over the years.
- Even more overt with the "Agent Venom" look for the symbiote, which downplays the "evil Lovecraftian spandex" look inherited from the symbiote's origins as a Spider-Man costume in favour of taking cues from military protective gear. His "Mk III" look◊ — used throughout Venom Vol. 2 — was even more "bio", sporting a more chitinous appearance with spines on his pauldrons, vambraces, and boots; H. R. Giger even being mentioned on the concept art as an influence.
- Venomverse introduces the Poisons, a species that possess and consume both symbiote and host on contact and take their powers. They end up with chitinous plate armor covering their bodies.
- Marvel Adventures: Iron Man gives Plant-Man a plant-based armor to better fight Iron Man's signature Powered Armor with.
- Spawn: The Hellspawn symbiotes — being demonic expies of the Venom symbiote and its ilk — cover their hosts in a black, red, and white bodysuit, and can manifest fanged jaws and a prehensile tongue. Al Simmons is bonded to one of these symbiotes, by the name of K7-Leetha, though its backstory has been repeatedly retconned over the course of the series.
- Darth Krayt, the main antagonist of Star Wars: Legacy wears a suit of Yuuzhan Vong armor, which, like all their tech, is organic.
- In Lords Among The Ashes, the Normans find that this was a form of Lost Technology used by the ancient civilization that existed before them on the Dark Continent. Jaune has the armor extensively analyzed to find that it has no effect on the user's soul and that it was enhanced by infusing metal armor with the flesh of Grimm.
- In Independence Day the small and physically frail aliens wear large and tentacled bio-suits that almost qualify as Mini-Mecha, though even then they can be knocked out by a sucker punch from Will Smith.
- A non-scientific example, in True Legend (2010), the Big Bad is a practitioner of the Venomous Fist, where upon reaching highest levels of his powers, gains a set of scorpion-like armour growing from his chest, shoulders and back, covering much of his body. In the penultimate confrontation with The Hero, the tide of battle is turned when the hero manage to rip off entire chunks of his organic armour leaving his flesh and internal muscle exposed in a ridiculously graphic manner.
- In the New Jedi Order series the Yuuzhan Vong wear "Vonduun crabs" as armor, which can stop blaster bolts and even lightsabers, but turned out to be fatally allergic to a type of tree pollen, which was later developed into a Synthetic Plague that could kill all Yuuzhan Vong and their "technology".
- God-Emperor Leto Atreides II from the Dune series wears a full-body suit composed of living sand-trout, turning himself into an immortal human-sandworm hybrid. His only weakness is being immersed in water, which is what happens at the end of God-Emperor of Dune.
- The "Eight Worlds" series of stories by John Varley includes a fascinating variant: an artificial creature called a Symb, short for "Symbiote", which is essentially a living spacesuit for a single human. A Symb needs only sunlight plus occasional doses of trace elements to sustain both itself and its human partner. It's not intelligent on its own, but it has the ability to 'plug into' its human partner's brain and form a separate personality therein.
- Living armor is one of Transcendent Technologies Inc's products in Hc Svnt Dracones. They allow their users to act like they have Reclamation surgeries, the TTI-Poltergeist even incorporates Transcendent tech, but if injured they have a habit of freaking out and sucking their users' blood.
- Being a Captain Ersatz of the Guyver, Cthulhutech's Tagers have shades of this. However, like everything in Cthulhutech, this trope gets the eldritch treatment.
- In SLA Industries, the alien Ebon and their related subspecies have black living armour called DeathSuits that give them various abilities. Interestingly the DeathSuits aren't organic in nature and are instead made of solidified Flux. The suits become living and semi-sentient only because of evolving from the presence of Flux in them and the symbiotic bond the suit has with its wearer.
- With technology devouring nanites circulating through the hair, humans are only able to fight robots with alien organic technology in Splicers. Humans are outfitted with armour made with biological material and DNA from various life-forms. As such abilities such as mighty insect legs growing out an armour's chest is a very real possibility.
- In Steamlogic's Mechanical Dream, there's a tribal race called the Yakis which has flesh-warpers take the placenta from a newly born Yakis and mold it into a symbiotic armour. Over time, various new powers develop such as flying wings and burrowing claws. Yakis, who had their armour destroyed or born in a place with no craftsmen capable of making armour, become pariahs in the tribe.
- In The Day After Ragnarok rpg setting one of the technologies developed from mining the corpse of the gigantic Midgard Serpent is the Ablative-Metabolic Suit. Made out of living snakeskin the wearer steps into and it immediately crawls over and seals itself. It can withstand every environmental temperature and pressure found on earth and is even an effective spacesuit.
- League of Legends:
- KaiSa was a normal human girl before being pulled into the Void, where she bonded with a symbiotic Voidling that formed a living bodysuit with biomechanical rocket pods on her shoulders.
- Kayn has a mix of this and Demonic Possession, caused by him wielding the living, evil scythe named Rhaast. In addition to whoever they're fighting, the two themselves are locked in a duel for control, so Rhaast has already visibly corrupted one of Kayn's arms and part of his face into a rough, demon-like form.
- [PROTOTYPE]: Alex Mercer's Armor power covers him in a black carapace that lets him plough through almost anything in his path. James Heller from [PROTOTYPE 2] doesn't have this power, but has an armored form as an alternate skin.
- Sigma Star Saga: The Krill wear living armor called a Parasite, which despite the name are completely harmless, and even beneficial since they enhance the wearer's physical capabilities. Humans can wear them just fine as well with no negative side effects.
- UFO Afterblank: Pops up in Aftermath's late-game, where the Reticulans all wore weird meaty-looking armour that came in several variants, some providing a brightly-coloured Deflector Shields bubble to protect the wearer and conveniently indicate the armour's variant. You could engineer your own hybrid armour. Both hybrid and reticulan bio-armour is lightweight and offers the best protection against energy weapons, but it's not quite as good against ballistic weapons as man-made armour.
- AsteroidQuest: Bio-armors are scored by a "mortality rate" value, since stronger bio-armors put more strain on the user. In practice the actual fatalities are much lower, because soldiers are tested first and simply don't put on bio-armor if they can't take it.