Here we present the first enzyme-triggered formation of indazoles via ring-closing N-N bond formation in a single catalytic reaction step. The NRs BaNTR1, NfsA and BmoNR were found to reduce nitro compounds to the reactive nitroso intermediates required for the spontaneous formation of indazoles. The NRs BaNTR1 and NfsA accept a range of polar and non-polar N-substitutions (1b-f) leading to the selective formation of 2Hindazoles. Primary amine substrates such as 1a and 1g lead to 1H-indazoles. Furthermore, NR-triggered indazole formation is applicable in enzymatic cascade reactions, as demonstrated in a two-step one-pot cascade starting with the formation of 1b from 12 and 14 using IRED15. This enzymatic cascade aborded the indazole 6b in 62 % isolated yield, demonstrating that 2H-indazoles can be accessed from cheap 2nitrobenzaldehydes and primary amines. Thus, the novel biocatalytic route reported herein not only expands the existing synthetic toolbox, but also represents an alternative to chemical and electrochemical methods, overcoming sustainability concerns and providing access to indazole derivatives and cinnoline. Ongoing research aims to optimize and extend cascade reactions using the NR-triggered N-N bond formation strategy presented in this work. In addition, further process engineering may be considered to increase the substrate concentrations of NR-triggered indazole formation.