The electrocatalytic nitrogen reduction reaction (ENRR) to ammonia is a potentially sustainable alternative to the Haber-Bosch (HB) process, but low Faradaic efficiencies and rates hinder its implementation. Perovskite oxynitrides are a tunable class of materials with unique chemistry for ENRR. Elucidating structure–property–mechanism relations for perovskite oxynitrides will aid ENRR catalyst design. © 2021 Elsevier Inc.