Background: Balamuthia mandrillaris is a free-living amoebic parasite that primarily causes rare opportunistic infections in immunocompromised hosts. Balamuthia amoebic encephalitis (BAE) is a rare yet severe parasitic infection affecting the central nervous system. It has an extremely low incidence in China but can have a mortality rate as high as 98%. The clinical manifestations of amebic infections are similar to those of bacterial and tuberculous meningitis, lacking specificity, which makes accurate diagnosis challenging in the clinical setting. Case Presentation: A 61-year-old immunocompetent woman experienced worsening headache and a moderate fever over the course of five days, initially treated as a common cold. On 25 February 2025, she exhibited behavioral abnormalities, dysphagia, and a high fever of 40.2 °C, which progressed to a coma. On 26 February, her cranial CT scan revealed multifocal hemorrhagic lesions in the right frontotemporoparietal lobes. The MRI revealed similar lesions with slight enhancement and herniation. She underwent an emergency decompressive craniectomy, yet her condition continued to deteriorate following the surgery. On 27 February, serum targeted next-generation sequencing (tNGS) detected B. mandrillaris. Additionally, metagenomic NGS (mNGS) of the cerebrospinal fluid (CSF) sample confirmed the presence on 28 February. Finally, B. mandrillaris was identified through a brain tissue biopsy on 3 March. However, due to the delayed diagnosis and lack of effective drugs, her condition rapidly deteriorated and became irreversible. Her family ultimately chose to withdraw treatment. Conclusions: This study highlights the application of NGS for early diagnosis of patients with severe CNS infection. Both tNGS and mNGS can be considered for the rapid detection of rare or novel pathogens and for facilitating diagnosis.