The EUMETSAT Meteosat Third Generation Lightning Imager (MTG-LI) is the brand-new European space-based lightning location system devoted to the diagnostic and characterization of lightning activity over hemispheric scale. In this publication, we present the assessment of MTG-LI detection performances against three different reference systems: the Vaisala Global Lightning Detection Network (GLD360), the European Consortium for Lightning Detection (EUCLID), and Geostationary Lightning Mappers (GLMs) -16 and -19 aboard NOAA GOES satellites. The analysis period is of eighteen months: from July 2024 to December 2025. MTG-LI flash detection efficiency varies between 70 % (day) and 95 % (night), with an average value of 87.4 %. Its average flash false alarm rate is generally below 0.5 flashes per second, while the average fraction of false flashes is 0.16 % of the total flashes. Finally, both average timing and location accuracy are presented and discussed.