We report on neutron diffraction, thermal expansion, magnetostriction, dielectric, and specific heat measurements on polycrystalline FeCr ₂S₄ in external magnetic fields. The ferrimagnetic ordering temperatures T_C ≈ 170K and the transition at T _OO ≈ 10K, which has been associated with orbital ordering, are only weakly shifted in magnetic fields up to 9T. The cubic lattice parameter is found to decrease when entering the state below T_OO. The magnetic moments of the Cr- and Fe-ions are reduced from the spin-only values throughout the magnetically ordered regime, but approach the spin-only values for fields >5.5T. Thermal expansion in magnetic fields and magnetostriction experiments indicate a contraction of the sample below about 60K. Below T_OO this contraction is followed by a moderate expansion of the sample for fields larger than ∼4.5T. The transition at T_OO is accompanied by an anomaly in the dielectric constant. The dielectric constant depends on both the strength and orientation of the external magnetic field with respect to the applied electric field for T < T_OO. A linear correlation of the magnetic-field-induced change of the dielectric constant and the magnetic-field dependent magnetization is observed. This behaviour is consistent with the existence of a ferroelectric polarization and a multiferroic ground state below 10K.