A 78-year-old male was referred to our facility due to persistent fever and arthralgia. Transesophageal echocardiography revealed fragile vegetations measuring 26 mm in length attached to the mitral valve (MV), along with severe mitral regurgitation. Magnetic resonance imaging showed multiple cerebral infarctions. He also had an abscess at his left sternoclavicular joint caused by Streptococcus agalactiae, which was identical to the strain identified in his blood culture. He was diagnosed with active infective endocarditis due to Streptococcus agalactiae and severe mitral regurgitation. To prevent postoperative mediastinitis, which could be a complication of median sternotomy in the presence of a left sternoclavicular joint abscess, he underwent urgent minimally invasive mitral valve surgery. Intraoperative Findings: The MV exhibited massive vegetation and partial valve destruction on the medial side of P2 and throughout P3, along with an annular abscess. The MV and annular abscess were debrided down to the left ventricular muscular layer. Mitral valve replacement was performed with reconstruction of the mitral posterior annulus using a bovine pericardial patch. The postoperative course was uneventful, and the left sternoclavicular joint abscess diminished with intravenous antibiotic therapy. He was discharged on the 36th day after surgery, and no relapse has been observed.