Water stress reduces germination and seedling emergence by compromising the metabolic activity of seeds. Associated with this, extreme thermal events have intensified, and temperatures above 30 °C can significantly reduce maize yield. In this scenario, the selection of tolerant genotypes is essential. This study evaluated the germination potential of 22 maize genotypes, including open-pollinated genotypes and commercial varieties. Seeds were characterized by moisture content, thousand-seed weight, germination, and emergence in the field. Subsequently, they were subjected to thermal stress of 5, 15, 25, 35, and 40 °C, through the adapted standard germination test. For water stress, the seeds were subjected to different water retention capacities (15, 30, 60, and 100%). The results indicated relevant genetic variation among the genotypes. For thermal stress, there was no germination at extreme temperatures (5 and 40 °C), while at 15 °C, there were significant differences between genotypes. At 35 °C, there was a reduction in vigor and an increase in abnormalities. Open-pollinated genotypes showed superior physiological performance under stress conditions. For water stress, at 15% there was low performance; at 30%, initial improvement; at 60%, ideal conditions with greater vigor; and at 100%, maintenance of performance, with little significant gains. Maize genotypes showed tolerance to water stress between 15% and 100% of the water retention capacity, with normal germination and seedling formation. Materials 3, 4, 8, 12, 16, and 20 showed greater tolerance to water restriction, while 2, 10, 14, 18, and 22 had better performance in more humid environments. Materials 7, 9, and 10 stood out for their greater vigor and germination. Regarding thermal stress, germination occurred between 15 °C and 35 °C, even outside the ideal range. Material 3 (AS1598) showed higher thermal tolerance, with better physiological performance, higher germination, and higher vigor.