This cross-sectional study tested the direct and stress-buffering effects of co-sleeping with pets on human sleep characteristics in a nationally-representative sample of United States adults. Participants completed questionnaires assessing their sleep characteristics, including perceived sleep quality, perceived sleep efficiency, insomnia severity, and multidimensional sleep health. We evaluated whether co-sleeping with pets was associated with sleep characteristics and whether co-sleeping with pets moderated the association of stress and sleep characteristics. Exploratory analyses examined whether sleep characteristics were impacted by number of pets, pet type, and bondedness to pets. Our final sample of 1591 participants (Mage = 46.4 years, SD = 17.5; 56% female; 76% White) included 758 participants who reported co-sleeping with pets (47.6%). Co-sleeping with pets was associated with poorer sleep characteristics—specifically, poorer perceived sleep quality and greater insomnia severity. Although higher levels of stress were associated with poorer sleep, we did not observe evidence for a stress-buffering effect of co-sleeping with pets. Exploratory analyses indicated that the negative impact of co-sleeping with pets on human sleep was associated with dog ownership but not cat ownership, more pronounced when individuals own a greater number of pets, and not impacted by bondedness to pets. Our findings contribute to emerging evidence for the impact of co-sleeping with pets on human sleep. Study was pre-registered at: https://aspredicted.org/3VN_WF6.