<p>Magnetic inorganic nanomaterials (MINs) exhibit tunable magnetic properties, high chemical stability, and versatile surface functionality, making them key materials for emerging applications in biomedicine and spintronics. This critical review summarizes and compares recent advances in synthesis strategies including physical, chemical, and bio-inspired routes that allow precise control over particle size, morphology, and magnetic performance. Key characterization techniques used to correlate structure with functionality are also discussed. In biomedical applications, MINs have shown strong potential as magnetic resonance imaging (MRI) contrast agents, targeted drug delivery carriers, hyperthermia mediators, and microrobots for minimally invasive therapies. In parallel, they play a crucial role in spintronic technologies such as giant magnetoresistance devices, magnetic tunnel junctions, and spin-torque oscillators, enabling high-density data storage and low-power electronics. Despite significant progress, challenges remain in achieving scalable and reproducible synthesis, ensuring long-term biosafety, standardizing magnetic performance metrics, and integrating MINs into multifunctional platforms. Finally, this review outlines future research directions, emphasizing interdisciplinary approaches that link material design, biological evaluation, and device engineering to facilitate the translation laboratory-scale advances into clinically and industrially viable technologies.</p>