The martial eagle (Polemaetus bellicosus) is a vulnerable species that is declining throughout large portions of its range. There is an urgent need to improve understanding of this species’ ecology to inform its conservation. I equipped 20 adult martial eagles with global positioning system backpack transmitters to characterize diet and space use of the species in the Maasai Mara region of Kenya. The resulting high-resolution transmitter data sets allowed for the rapid location of kills and provided a means to estimate home range size. From November 2016 to April 2018, 191 kills were identified from 206 kill location visits. Martial eagle diet comprised 26 prey species of which hares (two Lepus species, 17.3%), impala fawns (Aepyceros melampus, 13.6%) and helmeted guineafowl (Numida meleagris, 12%) were the most numerous. Sex-based differences in diet were found, with females selecting for heavier prey items (p < 0.001). The average 95% kernel density estimated home range for the duration-of-transmitter-placement (average of 372 days) was 174.5 ± 83.2 km2, a much larger estimate than previously reported. This study is the most extensive to date on martial eagle diet and spatial ecology in eastern Africa, and the first to show dietary differences between the sexes.