Context. NRAO 150 is one of the brightest radio and mm AGN sources in the northern sky, and is an interesting source to study extreme relativistic jet phenomena. However, its cosmological distance has not yet been calibrated, because of its optical faintness due to strong Galactic extinction. Aims: We measure the redshift of NRAO 150, to enable us to perform quantitative studies of the source. Methods: We conducted spectroscopic and photometric observations of the source in both the near-IR and the optical. Results: All these observations were successful in detecting the source. The near-IR spectroscopic observations exhibit strong Hα and Hβ emission lines from which the cosmological redshift of NRAO 150 (z = 1.517 ± 0.002) is determined for the first time. We classify the source as a flat-spectrum radio-loud quasar, for which we estimate a high supermassive black-hole mass ~5 × 109 M_&sun;. After extinction correction, the new near-IR and optical data show a high-luminosity continuum-emission excess in the optical (peaking in the rest frame at ~2000 Å) that we attribute to thermal emission from the accretion disk for which we estimate a high accretion rate of ~30% the Eddington limit. Conclusions: Comparison of the source properties and its broad-band spectral-energy distribution with those of Fermi blazars allows us to predict that NRAO 150 is among the most powerful of blazars, and hence a high luminosity - although not yet detected - γ-ray emitter. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.