The "Methane Emissions Mitigation Research and Development Act" establishes a comprehensive program to enhance the detection, quantification, and mitigation of methane emissions. It directs the Secretary of Energy to conduct research, provide technical assistance , and establish publicly accessible best practices for preventing and responding to methane releases across natural gas infrastructure and in coal mines. This includes supporting research into advanced technologies for more accurate methane quantification, such as improvements in data analytics, machine learning, and remote sensing. The bill mandates the establishment of a Methane Emissions Measurement and Mitigation Research Consortium within one year. This Consortium will foster data sharing, prioritize research, and develop cooperative leak detection and repair strategies among diverse stakeholders, including federal agencies, industry, and academia. Its responsibilities include developing a multiyear plan with technical goals and improving the understanding of methane emissions through enhanced detection, measurement, and mitigation capabilities. Additionally, the Secretary of Commerce, through the National Institute of Standards and Technology (NIST), will establish national facilities for testing and intercalibration of methane measurements. These facilities will advance detection, quantification, and relevant standards, providing high-resolution data and facilitating rapid performance testing of new measurement technologies under various conditions. The bill authorizes substantial appropriations for both the Department of Energy's programs and NIST's facilities from fiscal years 2026 through 2030 and beyond.