Abstract Lightning is a major source of nitrogen oxide radicals (NOx ≡ NO + NO2), but large uncertainties in NOx yields per flash hinder accurate quantification of emissions and impacts on oxidant chemistry. We use 1 year of concurrent geostationary satellite observations of free tropospheric (FT) NO2 from TEMPO and flash rates from GLM to show that lightning is the dominant source of FT NOx over North America. The observed FT NO2 and its correlation with flash rates imply a NOx yield of 150 ± 60 mol N flash−1. Applying this yield globally in the GEOS‐Chem atmospheric chemistry model reduces lightning NOx emissions from 6.6 to 3.2 Tg N yr−1. This generally improves simulated NOx, ozone, and hydroxyl radical in comparison with satellite and in situ measurements, though with some regional overcorrections for ozone. The methane lifetime against tropospheric OH increases from 8.7 to 9.4 years, partially reducing the gap with the best empirical estimate (11 years).