First-order magnetic phase transitions (FOMTs) have garnered extensive interest due to the coupling among lattice, spin, and electron degrees of freedom, which frequently manifests as abrupt magnetization jumps, phase coexistence, and anomalous transport phenomena. In this work, we report the observation of a FOMT in a distorted kagome metal ${\mathrm{Pr}}_3{\mathrm{MnBi}}_5$. Meanwhile, comprehensive measurements of magnetization, specific heat, and electrical transport reveal successive anomalies below 50 K, indicating a complex magnetic landscape. Notably, a pronounced first-order transition occurs at 25 K, as evidenced by the clear discontinuity and thermal hysteresis in both temperature-dependent magnetization and resistivity. Low-temperature x-ray diffraction reveals a volume anomaly across 25 K without a change in crystal symmetry, further confirming the FOMT nature. The magnetic states, transport behavior, and FOMT can be well manipulated by an external magnetic field, which underscores a significant spin-lattice and electron-lattice coupling effect. Furthermore, due to the quasi-one-dimensional geometry, ${\mathrm{Pr}}_3{\mathrm{MnBi}}_5$ exhibits strong magnetic anisotropy with in-plane easy magnetization. A pronounced positive magnetoresistance (68%) is presented in its low-temperature ferromagnetic ground state. These findings establish ${\mathrm{Pr}}_3{\mathrm{MnBi}}_5$ as a compelling distorted kagome platform for investigating the intricate interplay among magnetic anisotropy, lattice geometry, and transport behavior.

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• Ferromagnetism
• First order phase transitions
• Magnetic anisotropy
• Magnetoresistance
• Kagome lattice
• Rare-earth magnetic materials
• Magnetization measurements
• Resistivity measurements