Microwave machining utilizes microwave-induced discharge to cause material removal. The current work investigates the discharge characteristics during machining of duplex stainless steel (thickness: 1.0 mm) inside a customized microwave applicator operating at 3.0 kW power and 2.45 GHz frequency. Thoriated tungsten (diameter: 1.6 mm) was employed as a pointed tool to trigger microwave-induced discharge in atmospheric conditions under preset tool-work gaps. Microwave-induced discharge was observed in the form of spark and arc but with a delay. It was observed that the spark and arc initiation instant varied even for the same processing conditions. The spark initiated, grew in area and collapsed within a short duration of the order of 40 ms. Long-lived arc initiated similarly but attained greater area and intensity and proceeded with pulsation in the arc area. Arc ceased at the end of the microwave exposure or an instant when the tool lost sharpness due to tool wear. Stochasticity in microwave-induced discharge was evident in microwave-induced discharge machining. Arc is primarily responsible for machining since the total spark duration was much less than the arc duration. Measures to reduce the stochasticity of microwave-induced discharge machining have been discussed.