The magnetization and resistivity of single crystals of the Zintl compound ${\mathrm{Eu}}_{14}{\mathrm{MnBi}}_{11}$ are measured as functions of temperature and applied magnetic field. The magnetization data show an apparent antiferromagnetic transition at ${T}_{N}=32\mathrm{K}$ even though the high-temperature susceptibility suggests that the exchange coupling is ferromagnetic in nature. The zero-field resistivity is approximately independent of temperature above 32 K. Below 32 K the resistivity increases slightly and peaks at about 20 K before decreasing as the temperature is decreased. This temperature dependence is fairly normal for an antiferromagnetic metal. On the other hand, in contrast to other antiferromagnets, the single-crystal magnetoresistance is large and negative at all temperatures below about ${3T}_{N}.$ In addition, the dependence of the resistivity upon the magnetization is quite similar to the colossal-magnetoresistance materials.