Thermoelectric (TE) materials directly transform thermal into electrical energy and vice versa, making them promising for a plethora of applications in refrigeration or power generation. However, state-of-the-art semiconductors in the focus of current TE research did not make the leap into broad applications due to their low power density and poor mechanical properties. Metallic systems would be superior in this regard, but remained largely neglected by the TE community over the past decades due to their small Seebeck coefficient S. Here we realize high TE performance in metals via tuning of electronic interband scattering. Using this paradigm, we discovered record-high power factors up to 34 mWm−1K−2 in binary NiAu alloys, exceeding previous benchmark values by several times [1]. The unusually high S in this metallic system, yielding the largest figure of merit zT ≈ 0.5 reported in metals so far, results from strongly electron-hole asymmetric charge transport. In the highly conductive s-band of NiAu the mobility of holes is selectively reduced by interband scattering from localized Ni d states below the Fermi energy. Our concept is generally applicable to various metallic compounds and alloys – also without expensive elements like Au. This new paradigm towards scattering-tuned ultrahigh TE performance in metals is cardinally different from tuning zT in semiconductors. Crucially, phonon heat transport is irrelevant in metallic systems due to the Wiedemann-Franz law, which confines the multi-parameter optimization problem of zT to a sole increase of S (in metals zT = S2/L; L is the Lorenz number). Finally, we present a roadmap of systematic electronic tuning of TE properties in metals via high-throughput computational materials screening. [1] F. Garmroudi, M. Parzer, A. Riss, C. Bourgès, S. Khmelevskyi, T. Mori, E. Bauer, and A. Pustogow, High thermoelectric performance in metallic NiAu alloys via interband scattering, Sci. Adv. 9, eadj1611, (2023) [2] Mahan, G.D., Sofo, J.O. The best thermoelectric. Proc. Natl. Acad. Sci. 93, 7436-7439, (1996)