Background: Bronchopleural fistula (BPF) following pneumonectomy is a catastrophic complication associated with sepsis, respiratory compromise, and high mortality. Management often requires close collaboration between cardiothoracic and reconstructive surgeons. When ipsilateral regional flaps or recipient vessels are unavailable due to prior thoracotomy, reconstructive options are limited. We describe a multidisciplinary strategy for intrathoracic salvage using free tissue transfer in a complex post-pneumonectomy BPF. Methods: A 63-year-old man developed a persistent BPF with chronic pleural sepsis following right pneumonectomy for non–small cell lung cancer. Prior ipsilateral thoracotomy rendered local pedicled flaps non-viable. A joint cardiothoracic–plastic surgery plan was developed to achieve fistula closure and pleural dead space obliteration. A contralateral free latissimus dorsi muscle flap was harvested and augmented with serratus anterior muscle based on its angular branch to provide adequate volume. Cardiothoracic surgeons facilitated intrathoracic access and preparation of internal mammary recipient vessels, enabling microsurgical anastomosis and controlled intrathoracic inset. Flap monitoring was performed using a skin paddle and implantable Doppler. Results: Close intraoperative collaboration was required due to limited exposure, altered thoracic anatomy, and respiratory considerations. The free muscle transfer successfully sealed the BPF and obliterated pleural dead space. Postoperatively, flap perfusion remained stable with no ischemia, infection, or recurrent air leak. Follow-up imaging confirmed durable fistula closure. Conclusion: Post-pneumonectomy BPF reconstruction requires multidisciplinary planning and adaptable reconstructive strategies. When ipsilateral options are unavailable, contralateral free muscle transfer provides a reliable intrathoracic salvage solution, highlighting the value of coordinated cross-specialty reconstruction.