Within-species variation is a salient feature of natural populations, of substantial importance for species interactions. However, the community consequences of sexual dimorphism, one of the most ubiquitous sources of within-species variance, remains poorly understood. Here, we extend classical models of consumer-resource dynamics to explore the ecological consequences of consumer sexual dimorphism. We show that sexual dimorphism in consumer attack rates on two different resource species promotes coexistence between those resources, mitigating the effects of both apparent competition and direct interspecific competition. Consumer sexual dimorphism can prevent exclusion of a resource with inferior growth rates because reduction in any of the two resources reduces consumer density, generating negative frequency dependence that stabilizes coexistence between resources. Our work highlights ecological sex differences as a potentially key factor governing the assembly of ecological communities, illustrating that the specific source of within-species variance can have important implications for community ecology.