Antimicrobial resistance, strict regulations on the use of antibiotics in livestock and consumer preference for sustainable livestock products have once again drawn attention to the role of medicinal plants as complementary or alternate means of treatment in the veterinary field. This review consolidates evidence from 151 peer-reviewed articles in order to critically analyze the possibilities in the use of phytomedicines in the context of One Health through an analysis of its therapeutic possibilities, disease management roles and even the conservation aspect. The history and ethnobotany behind the use of plants in animal therapy is explored, along with the pharmacology behind the major bioactive principles alkaloids, flavonoids, terpenoids, essential oils and tannins discussing their mode of action that include cell membrane disruption, efflux-pump inhibitors, quorum-sensing inhibitors and immune modulation. Specific examples exist from studies involving species across livestock, companion and aquatic animals as well as captive and free-ranging wildlife that show antimicrobial, antiparasitic anti-inflammatory and wound healing properties, among others, with multi-target effects suggesting a possible approach for minimizing resistance development. The review highlights the trade-offs associated with the exploitation of botanical resources, focusing on conservation practices through cultivation efforts and community management, as well as current barriers to the development of plant medicine, which include lack of standardization, pharmacokinetic information, clinical studies and regulation. The review highlights that for moving forward from using veterinary phytotherapeutics in an empirical way to applying them scientifically, there is a need for concerted efforts toward conducting proper clinical trials, pharmacology research on animals, toxicity testing and regulation of the use of medicinal plants.