Objective: To describe patterns of sedentary behaviour and physical activity in adults two weeks post-hospital discharge following an upper or lower limb fracture, and identify associated predictive factors. Design: Observational study. Setting: Level 1 Trauma Centre. Participants: Adults aged 18–69 years with an isolated upper (UL) or lower (LL) limb fracture. Main Outcome Measures: Sitting time and steps measured via a triaxial accelerometer and inclinometer-based device (activPAL) (anterior thigh); and moderate-intensity physical activity (MPA) measured via triaxial accelerometer (ActiGraph) (hip) for ten days. Results: Of 83 participants, 63% were men and 55% had sustained LL fractures; mean (SD) age was 41 (14) years. Participants sat for a mean (SD) of 11.07 (1.89) h/day, took a median (IQR) of 1575 (618–3445) steps/day and had only 5.22 (1.50–20.78) mins/day of MPA. Multivariable regression analyses showed participants with LL fracture, had increased adjusted mean sitting time of 2.5 h/day relative to UL fracture (β = 2.5 hours, p < 0.001). For each day since surgery/injury there was reduced adjusted mean sitting time of 4 mins/day (β = −0.06 hours, p = 0.048). LL fracture was associated with 80% fewer steps/day (Ratio of Geometric Means (RGM) = 0.20, p < 0.001) and 89% less MPA (RGM = 0.11, p < 0.001) relative to UL fracture. Older age was associated with 59–62% less MPA relative to the youngest participants (RGM = 0.38–0.41, p = 0.01). There was no association between the predictive variables sex, BMI and pre-injury physical activity and any outcome. Conclusions: At two weeks post-hospital discharge, participants were engaged in high amounts of sitting and were physically inactive. Injury location was the strongest predictor of outcome, indicating that patients with LL fracture are most in need of encouragement to reduce sitting time and gradually increase activity, within the bounds of clinical safety.