Recent experimental data on the optical conductivity of niobium-doped SrTiO₃ are interpreted in terms of a gas of large polarons with effective coupling constant αeff ≈2. The theoretical approach takes into account many-body effects, the electron-phonon interaction with multiple LO-phonon branches, and the degeneracy and the anisotropy of the Ti t _2g conduction band. Based on the Fröhlich interaction, the many-body large polaron theory provides an interpretation for the essential characteristics, except-interestingly-for the unexpectedly large intensity of a peak at ∼130 meV, of the observed optical conductivity spectra of SrTi _1-xNb_xO₃ without any adjustment of material parameters.