Semiconductor nanowires have shown great potential for enabling ultracompact lasers for integrated photonics platforms. Despite the impressive progress in developing nanowire lasers, their integration into Si photonics platforms remains challenging largely because of the use of III-V and II-VI semiconductors as gain media. Recently, group IV nanowires, particularly direct bandgap GeSn nanowires capable of emitting above 2 μm, have emerged as promising cost-effective gain media for Si-compatible nanowire lasers, but there has been no successful demonstration of lasing from this seemingly promising nanowire platform. Herein, we report the experimental observation of lasing above 2 μm from a single bottom-up grown GeSn nanowire. By harnessing strain engineering and optimized cavity designs simultaneously, the single GeSn nanowire achieves an amplified material gain that can sufficiently overcome minimized optical losses, resulting in single-mode lasing with an ultralow threshold of ~5.3 kilowatts per square centimeter. Our finding paves the way for all–group IV mid-infrared photonic-integrated circuits with Si-compatible lasers for on-chip classical and quantum applications.