Introduction Work-life balance (WLB) is a critical concern for emergency medical technicians (EMTs) because it significantly affects the provision of comprehensive emergency medical services (EMS). This study investigated personal and work-related factors influencing work-to-family negative spillover (WFNS), a key element of WLB, among EMTs. Methods A web-based survey was conducted from July 26 to September 13, 2021, among EMTs in Hokkaido, Japan. The study included 21 facilities that were randomly selected from 42 fire stations. The Japanese version of the Survey Work-Home Interaction-NijmeGen (SWING-J) was used to measure WFNS. Personal background factors, such as age, sex, years of work experience, and education, were surveyed. We also evaluated work environment factors, such as weekly working hours, monthly night shifts, monthly overtime hours, and yearly paid vacation days. Unpaired Student's t-tests, one-way analysis of variance (ANOVA), and multilevel generalized linear model (MGLM) analyses were used to explore the relationships between WFNS and personal and work-related factors. Results A total of 912 respondents were included in our analysis. They were predominantly male (98.2%), with an average EMT work experience of 12.7 years and a mean WFNS score of 1.16 (standard deviation (SD) = 1.67). MGLM analysis, adjusting for covariates, identified years of work experience (β = -0.129, p = 0.001), monthly overtime hours (β = 0.184, p < 0.001), and yearly paid vacation days (β = -0.170, p < 0.001) as independent factors associated with WFNS. Conclusion This study suggested that adjusting WFNS among EMTs could be achieved by reducing overtime hours and fostering an organized approach to paid leave within the work environment.