Selective catalytic ammonia-to-dinitrogen oxidation (NH3-SCO) is highly promising for the abatement of NH3 emissions from flue gas purification devices. However, there is still a lack of high-performance and cost-effective NH3-SCO catalysts for real applications. Here, highly dispersed, electron-deficient Cu-based catalysts were fabricated using nitrogen-doped carbon nanotubes (NCNT) as support. In NH3-SCO catalysis, the Cu/NCNT outperformed Cu supported on N-free CNTs (Cu/OCNT) and on other types of supports (i.e., activated carbon, Al2O3, and zeolite) in terms of activity, selectivity to the desired product N2, and H2O resistance. Besides, Cu/NCNT demonstrated a better structural stability against oxidation and a higher NH3 storage capacity (in the presence of H2O vapor) than Cu/OCNT. Quasi in situ X-ray photoelectron spectroscopy revealed that the surface N species facilitated electron transfer from Cu to the NCNT support, resulting in electron-deficient Cu catalysts with superior redox properties, which are essential for NH3-SCO catalysis. By temperature-programmed surface reaction studies and systematic kinetic measurements, we unveiled that the NH3-SCO reaction over Cu/NCNT proceeded via the internal selective catalytic reaction (i-SCR) route; i.e., NH3 was oxidized first to NO, which then reacted with NH3 and O2 to form N2 and H2O. This study paves a new route for the design of highly active, H2O-tolerant, and low-cost Cu catalysts for the abatement of slip NH3 from stationary emissions via selective oxidation to N2.