This review focuses on the state‐of‐the‐art of solid‐state lighting devices (SSLDs)—that is, organic light‐emitting diodes (OLEDs) and light‐emitting electrochemical cells (LECs)—prepared with transition metal complexes featuring thermally activated delayed fluorescence (TADF) mechanism. First, the TADF mechanism is briefly introduced, as well as the experimental and theoretical methods applied to study TADF in transition metal complexes. Second, the review presents an exhaustive overview of OLED and LEC devices incorporating organometallic TADF emitters. For each type of device, the description of TADF is organized by respective elements focusing on each emission color, that is, blue, green/yellow, orange/red and, if existing, white. Finally, insights and future potential development of organometallic TADF emitters for lighting devices are comprehensively discussed. Overall, this review complements recent ones focused on TADF small molecules applied to the SSLD field.