BACKGROUND Traditionally, men are not supposed to take part in maternal health issues in many cultures. Nevertheless, pregnancy care and childbirth are the most crucial matters of reproductive health influenced by men. Hence, the aim of this study was to identify individual, sociocultural, and health facility factors affecting men's involvement in facility-based childbirth in Southwest, Ethiopia. OBJECTIVE The aim of this study was to identify individual, sociocultural, and health facility factors affecting men's involvement in facility-based childbirth in Southwest, Ethiopia. METHODS A community-based cross-sectional study accompanied with a qualitative method was carried out from 1 July to 30 August 2019. A multistage cluster sampling technique was employed to recruit study participants. Descriptive statistics, frequencies, proportions, and mean were calculated, and the results of the analysis were presented in text, tables, and graphs. A multivariate logistic regression model was fitted to investigate the independent effect of each explanatory variable on the likelihood of men's involvement in facility-based childbirth. Qualitative data were analyzed thematically using OpenCode 4.0 software. RESULTS Out of 800 men, only 36.5% (95% confidence interval: 33.3%-39.6%) were found to have involved in facility-based childbirth. Several factors were associated with men's involvement in facility-based childbirth of this, being in the age group of 40-49 (adjusted odds ratio 5.04, 95% confidence interval: 2.49-10.20), attaining secondary education and above (adjusted odds ratio 2.14, 95% confidence interval: 1.53-5.60), and having sufficient knowledge of danger signs during pregnancy (adjusted odds ratio 5.65, 95% confidence interval: 3.25-7.46) associated with men's involvement in facility-based childbirth. CONCLUSIONS Relevant entities had better design-specific educational programs targeting younger age groups, those with lower schooling, and had previous bad obstetrics outcomes. Involving elders and religious leaders in the reproductive health program could also help in overcoming the existing cultural barriers. Moreover, creating a men-friendly facility environment and extensively engaging medias are suggested to improve men's involvement in the study area.