A processor including instruction support for implementing large-operand multiplication may issue, for execution, programmer-selectable instructions from a defined instruction set architecture (ISA). The processor may include an instruction execution unit comprising a hardware multiplier datapath circuit, where the hardware multiplier datapath circuit is configured to multiply operands having a maximum number of bits M. In response to receiving a single instance of a large-operand multiplication instruction defined within the ISA, wherein at least one of the operands of the large-operand multiplication instruction includes more than the maximum number of bits M, the instruction execution unit is configured to multiply operands of the large-operand multiplication instruction within the hardware multiplier datapath circuit to determine a result of the large-operand multiplication instruction without execution of programmer-selected instructions within the ISA other than the large-operand multiplication instruction.