The increasing demand for sustainable infrastructure, coupled with the need for materials that can withstand aggressive environments, has driven researchers to develop highperformance concrete with reduced carbon emissions and enhanced durability. This study is undertaken to address these challenges by exploring the mechanical performance, workability, microstructural behavior, and environmental impact of ultra high-performance concrete (UHPC) incorporating supplementary cementitious materials (SCMs) such as fly ash, ground granulated blast furnace slag (GGBFS), and microfine particles. Six UHPC trial mixes (TM01–TM06) were developed with a fixed water-to-binder ratio of 0.2 and evaluated through compressive, split tensile, and flexural strength tests at 7, 28, and 56 days. TM04, which included steel fibers, achieved the highest mechanical performance, showing a 25 % increase in compressive strength and a 20-30 % improvement in tensile and flexural strength compared to fiber-free mixes. Workability was assessed using slump flow tests, where TM01 and TM02 showed better flow retention (~5 % loss), while TM06 experienced a 9 % drop due to the presence of steel fibers. SEM analysis confirmed that TM04 exhibited a denser microstructure with uniformly distributed N-A-S-H and C-AS-H gels and reduced porosity, while TM01 showed scattered gel formations and micro-voids. In terms of environmental impact, TM04 and TM05 containing higher SCM content with 40 % cement reduction achieved up to 35 % lower carbon emissions compared to TM01. Life cycle assessment (LCA) results also showed that TM03 achieved an 18 % reduction in embodied CO2 emissions (E-CO2). These findings highlight the potential of SCM- and fiber-enhanced UHPC mixes to deliver high strength, improved durability, and reduced environmental footprint, making them suitable for modern, sustainable construction applications.