Background <p>This systematic review examines the relationship between habitual physical activity (PA) in mid-life and fracture outcomes.</p> Objectives <p>To determine whether habitual physical activity undertaken in mid-life is associated with the risk of fractures occurring at any later time.</p> Methods <p>We searched PubMed, CINAHL, and Embase (from inception to May 2025) and included non-experimental studies reporting a relationship between habitual physical activity undertaken in mid-life and a subsequent fracture. Risk of bias was assessed using the Newcastle–Ottawa Scale, and certainty of evidence was established with the GRADE approach.</p> Results <p>From 1779 abstracts, we included 10 cohort studies and 3 case-control studies. There was high variation in how physical activity was measured and categorised across studies, limiting comparability. Due to study heterogeneity in exposure and outcome reporting, we conducted a synthesis without meta-analysis (SWIM). Following the GRADE approach, we found low certainty of evidence for a protective effect of moderate activity in mid-life on hip fracture in men (<i>n</i> = 2) and moderate certainty of evidence for a protective effect of high physical activity in mid-life on hip fracture in women (<i>n</i> = 4). There was very low certainty of evidence for the effect of either moderate or high activity on other types of fracture outcomes in men or women (<i>n</i> = 3). Qualitative review of two large studies of moderate to high quality provided further support for these findings.</p> Conclusions <p>The temporal relationship between physical activity intensity in mid-life and subsequent fracture risk remains unclear. Further studies using device-measured physical activity and detailed time-to-event data are required.</p>