<p>Thermal energy has become an increasingly severe environmental stressor to cash crop production worldwide because of global warming. Annexins, proteinaceous protectants against abiotic stress, are multifunctional proteins capable of peroxidase- and Ca²⁺-dependent and Ca²⁺-independent binding to or insertion into membranes. Annexins in plants belong to the annexin D family and are further clustered into six phylogenetic clades on the basis of their structural diversity. A previous study in peanut identified six <i>annexins</i>, but their thermotolerance functions remain unknown. In this study, we report that <i>AhANN6</i>, a peanut <i>annexin</i>, confers heat resistance in <i>Escherichia coli</i> and <i>Arabidopsis</i> when overexpressed. <i>AhANN6</i> expression led to positive responses to drought stress, ABA supplementation, and heat stress in leaves and was developmentally regulated during germination and pegging. The AhANN6-YFP fusion protein was targeted to the plasma membrane of tobacco cells, suggesting that AhANN6 is localized in the cell membrane. <i>AhANN6</i>-overexpressing <i>E. coli</i> exhibited better growth under heat stress and oxidative stress, validating the molecular function of AhANN6 against abiotic stress. <i>AhANN6</i>-overexpressing <i>Arabidopsis</i> also presented increased heat resistance during vegetative growth. The decreased response of electrolyte leakage in the transgenic <i>Arabidopsis</i> to heat stress indicates potentially improved membrane stability as a result of AhANN6 overexpression. Additionally, the overexpression of <i>AhANN6</i> in <i>Arabidopsis</i> led to increased expression of <i>AtPOD</i> and <i>AtAPX</i>, key enzyme-encoding genes involved in ROS scavenging, suggesting that <i>AhANN6</i> is involved in maintaining ROS detoxification. Our findings suggest that AhANN6 plays a crucial role in protecting cell membrane integrity and promoting vegetative growth under adverse environmental stressors.</p>