Background: Upper limb lymphoedema is a chronic condition arising from diverse aetiologies, including primary lymphatic dysfunction and secondary causes such as malignancy-related and other post-operative lymphatic disruption, trauma, and infection. While lymphatic drainage patterns and disease severity are well described in breast cancer-related lymphoedema, data in non-breast-cancer-related upper limb lymphoedema remain limited. Improved characterisation of lymphatic anatomy may inform surgical planning and postoperative management. Methods: A retrospective cohort study was conducted at a tertiary Australian lymphoedema centre. Adults with non-breast-cancer-related upper limb lymphoedema who underwent indocyanine green (ICG) lymphography between 2017 and 2024 were included. Lymphatic drainage regions and disease severity were assessed using the MD Anderson Cancer Center (MDACC) staging system. Associations between severity and age, sex, and body mass index (BMI) were explored. Results: Twenty-six participants (27 limbs) were analysed. Aetiologies included primary lymphoedema, malignancy-related lymphoedema (commonly melanoma), post-operative lymphatic dysfunction, trauma, infection, and lymphoedema of unknown cause. The ipsilateral axilla was the predominant drainage region (81.5%). Drainage variability increased with severity. Mild to moderate lymphoedema (MDACC stages 1–2) was observed in 66.6% of limbs, while 33.3% were moderate to severe (stages 3–5). Older age, male sex, and obesity were associated with higher odds of severe disease, although not statistically significant. Conclusion: Non-breast-cancer-related upper limb lymphoedema most commonly drains to the ipsilateral axilla, with increasing variability in drainage pathways as severity progresses. These findings are consistent with breast cancer-related lymphoedema and highlight the relevance of axillary lymphatic anatomy to surgical decision-making and multidisciplinary management across diverse aetiologies.