Extremely large magnetoresistance (XMR) observed in topological materials holds significant promise for spintronic applications. In this work, we systematically investigate the magnetotransport properties and quantum oscillations in high-quality single crystals of the magnetic nodal-line semimetal ${\mathrm{FeGe}}_2$. Synthesized via chemical vapor transport, the ${\mathrm{FeGe}}_2$ crystals exhibit an exceptional residual resistivity ratio of 533 and achieve a nonsaturating XMR of $\mathrm{23 000}\%$ at 1.8 K and 14 T, accompanied by ultrahigh carrier mobility ($1\times {10}^5{\text{cm}}^2{\text{V}}^{-1}{\text{s}}^{-1}$). Shubnikov-de Haas oscillations reveal a $\pi$-Berry phase, suggesting a possible nontrivial topological nature of ${\mathrm{FeGe}}_2$. The remarkably high ratio of transport-to-quantum lifetimes (${\tau }_{\text{tr}}/{\tau }_Q\approx 1571$) further confirms suppression of backscattering, possibly related to topological protection. Combined with Hall effect measurements and extended Kohler scaling analysis, we establish that the origin of XMR in ${\mathrm{FeGe}}_2$ arises from the synergistic interplay between topological protection and high carrier mobility, rather than conventional electron-hole compensation. These findings not only provide critical experimental insights into the XMR mechanism of magnetic nodal-line semimetals but also highlight ${\mathrm{FeGe}}_2$ as a promising candidate for designing next-generation topological spintronic devices.

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• Magnetoresistance
• Shubnikov-de Haas effect
• Nodal-line semimetals