The influence of alloying additions on the microstructure, mechanical, and magnetic properties of bulk Fe79B20Cu1, Fe79B16Ti4Cu1, Fe79B16Mo4Cu1 and Fe79B16Mn4Cu1 (at. pct) alloys was investigated. Nanocrystalline samples in the form of 3 mm rods were prepared directly by suction casting without additional heat treatment. Mössbauer spectroscopy, transmission electron microscopy and scanning electron microscopy studies confirmed that the investigated alloys consist α-Fe and Fe2B nanograins embedded in an amorphous matrix. The addition of alloying elements, such as Ti, Mo and Mn to Fe79B20Cu1 alloy increases the amount of amorphous phase and decreases the presence of Fe2B phase in all examined alloys. The mechanical properties of the samples, such as hardness, elastic modulus, and elastic energy ratio, were analysed by an instrumented indentation technique performed on a 12 × 12 nanoindentation grid. These tests allowed to characterise the mechanical properties of the regions observed in the same material. For the Fe79B20Cu1 alloy, the hardness of 1508 and 1999 HV, as well as Young’s modulus of 287 and 308 GPa, were estimated for the amorphous- and nanocrystalline-rich phase, respectively. The addition of Ti, Mo, and Mn atoms leads to a decrease in both hardness and elastic modulus for all regions in the investigated samples. Investigations of thermomagnetic characteristics show the soft magnetic properties of the studied materials. More detailed studies of magnetisation versus magnetic field curves for the Fe79B20−xMxCu1 (where x = 0 or 4; M = Ti, Mo, Mn) alloy, recorded in a wide range of temperatures, followed by the law of approach to magnetic saturation revealed the relationship between microstructure and magneto-mechanical properties.