Purpose: Giant ovarian cysts causing iliofemoral deep vein thrombosis (DVT) through inferior vena cava (IVC) compression are exceptionally rare. Standard interventions, including IVC filter placement, may be contraindicated when cyst malignancy cannot be excluded. We report a novel single-stage hybrid operative approach for simultaneous mechanical thrombectomy and salpingo-oophorectomy in this setting. Methodology: An 18-year-old woman presented with a five-day history of acute left lower-limb swelling. Investigations confirmed extensive left iliofemoral DVT and a 33 cm unilocular ovarian cyst with complete IVC effacement. Following multidisciplinary review, a hybrid theatre operation was planned: catheter-directed mechanical thrombectomy using a ClotTriever device (Inari Medical), ultrasound-guided cyst decompression, and laparoscopic left salpingo-oophorectomy performed in a single session. Results: Thrombectomy achieved complete clot clearance. An intraoperative May-Thurner variant was identified; iliac vein stenting was deferred given the patient's age and multifactorial aetiology. Postoperative surveillance duplex at one month confirmed no residual thrombus. Histopathology returned benign serous cystadenofibroma. The patient was transitioned to a direct oral anticoagulant (DOAC) for three months with rapid resolution of symptoms and no complications. Conclusion: A single-stage hybrid approach combining mechanical thrombectomy and salpingo-oophorectomy is feasible, safe, and effective for extensive iliofemoral DVT caused by giant ovarian cyst-mediated IVC compression. This case supports multidisciplinary hybrid theatre planning when conventional management is contraindicated and may guide similar complex presentations.