The underlying mechanism for non‐oxidative methane aromatization remains controversial owing to the lack of experimental evidence for the formation of the first C−C bond. For the first time, the elementary reaction of methane with atomic clusters (FeC3−) under high‐temperature conditions to produce C−C coupling products has been characterized by mass spectrometry. With the elevation of temperature from 300 K to 610 K, the production of acetylene, the important intermediate proposed in a monofunctional mechanism of methane aromatization, was significantly enhanced, which can be well‐rationalized by quantum chemistry calculations. This study narrows the gap between gas‐phase and condensed‐phase studies on methane conversion and suggests that the monofunctional mechanism probably operates in non‐oxidative methane aromatization. Generation of acetylene, the C−C coupling product in the high‐temperature reaction of methane with atomic cluster species (FeC3−), has been identified. This provides a molecular level origin of the monofunctional mechanism for non‐oxidative methane aromatization proposed in condensed phase systems.