This study examined firefighters' sleep quantity and quality throughout multi-day wildfire suppression, and assessed the impact of sleep location, shift length, shift start time, and incident severity on these variables. For four weeks, forty-one volunteer firefighters sleep was assessed using wrist actigraphy. Analyses revealed that the quantity of sleep obtained on fire days was restricted, and pre- and post-sleep fatigue ratings were higher, compared to non-fire days. On fire days, total sleep time was less when: i) sleep location was in a tent or vehicle, ii) shifts were greater than 14 h, and iii) shifts started between 05:00-06:00 h. This is the first empirical investigation providing objective evidence that firefighters' sleep is restricted during wildfire suppression. Furthermore, sleep location, shift length, and shift start time should be targeted when designing appropriate controls to manage fatigue-related risk and preserve firefighter health and safety during wildfire events. Practitioner Summary During multi-day wildfire suppression, firefighters' sleep quantity was restricted, and pre- and post-sleep fatigue ratings were higher, compared to non-fire days. Furthermore, total sleep time was less when: i) sleep occurred in a tent/vehicle, ii) shifts were >14 h, and iii) shifts started between 05:00-06:00 h.