People with a spinal cord injury (SCI) report less physical activity than other populations and may engage in more sedentary behaviour (SB), especially sitting time. SB negatively impacts physiological and psychosocial outcomes in the general population, yet minimal research has explored the effects in people with SCI. The goal of this scoping review was to catalogue and describe the effects of acute SB among people with SCI. We searched four databases before February 2024 for studies in which people with any SCI sat, laid, or reclined for more than one hour in a day, and any physiological, psychological, or behavioural (i.e., SB time) outcome was measured. In total, 2021 abstracts were screened, and eight studies were included (n = 172 participants). The studies were characterized by varied definitions, manipulations, and measures of SB. Most measured outcomes were physiological (e.g., metabolic, blood pressure), followed by behavioural (e.g., SB time) and psychological (e.g., well-being, affect). When SB was interrupted, only postprandial glucose and affect improved. Based on two studies, participants engaged in 1.6 to 12.2 h of SB per day. Average uninterrupted wheelchair sitting bouts lasted 2.3 h. Based on the very limited body of research, it is impossible to draw any conclusions regarding the nature, extent, or impact of SB in people with SCI. There is much work to carry out to define SB, test its effects, and determine if and how people with SCI should reduce and interrupt SB.