The issues faced by CMOS technology in the nanoregime have led to research for other possible technologies that can operate with the same functionalities but with higher speed and lower power dissipation. One such technology is quantum-dot cellular automata (QCA). A 3  ×  3 reversible universal and multifunctional gate is presented that is reversible, universal, and multifunctional in nature. The gate is then used as a building block to design an ultra-efficient 1-bit full adder and 1-bit full subtractor in QCA. Based on the performance analysis, it is concluded that the proposed designs are efficient in respect to cell count, area, delay, and quantum cost and achieve performance improvements over existing designs in the literature. Hence, the proposed designs can be efficiently utilized in various digital logics requiring minimal area and ultra-low-power consumption such as central processing units, microcontrollers, etc.