Harmful alcohol consumption is shaped by a complex range of structural, social, and individual determinants that interact with inequality axes, which can be addressed at the community level. Under the framework of Barcelona Health in the Neighborhoods, which is a community strategy to reduce health inequalities in Barcelona’s most deprived neighborhoods, a community steering group will co-design a multicomponent community intervention. Aims: to assess its effects on: (1) alcohol accessibility, availability, and consumption at the environmental level, and (2) psychosocial and cognitive determinants of harmful alcohol consumption at the individual level. Methods: Quasi-experimental design with a comparison group, and pre- and post-intervention measures. Three Barcelona neighborhoods will be assigned to the intervention or comparison group based on three criteria: healthcare data on alcohol use, socioeconomic characteristics, and population size. The intervention includes activities promoting community mobilization, law enforcement, and communication campaigns in the intervened neighborhoods. Non-participant observations in standardized census sections will be performed in public spaces to collect information on three outcomes: alcohol accessibility, availability, and signs of alcohol consumption. Data collection includes a survey to a sample of 622 subjects to detect differences on these outcomes: risk awareness, knowledge, and self-efficacy about harmful alcohol consumption and drinking patterns. Discussion: This protocol to assess the effects of a multicomponent community intervention on harmful alcohol consumption at the environmental and population level will provide evidence on effective community health interventions and enable informed decisions for policy makers. This protocol could also be used as an implementation guide for studies aimed at reducing harmful drinking in cities with similar characteristics.