Background: To establish evidence for the validity of the Sedentary Behavior Record (SBR) instrument using a criterion measure through a proxy of direct observation. Methods: A total of 27 study participants (aged ≥18 y; 15 male) participated in this study. Throughout a 4-day measurement period, each participant recorded their sedentary behavior using the SBR in 10-minute blocks every night. During the measurement period, participants also wore wearable Autographer cameras as a proxy for direct observation. Autographer data were aggregated into 10-minute intervals. To establish evidence of validity, contingency (C) and Kappa (K) coefficients were calculated between the SBR and the Autographer data. For C and K, agreements were determined between 2 measures every cell. The coefficient C was compared across domains, types, and time of day, and K was compared across types of day and times of day. Results: Overall, the coefficients C and K were acceptable (C = .70) and substantial (K = .64), respectively. Among all domains, the highest C was reported for work-related sitting (C = .87). Values of C ranged from .49 to .91 among all activities; the highest accuracy was for work-related, screen-based sitting. Conclusions: This study suggests that the SBR is an acceptable self-report measure of sedentary behavior in adults.