Future wearable technologies and personal electronics may benefit from e‐textiles that simultaneously possess high elasticity and multiple capabilities such as energy harvesting and sensing. Here, the first elastic multifunctional fiber that can scavenge mechanical energy from body motion and electromagnetic energy from surrounding electrical appliances is presented. In addition to converting multiple sources of waste energy into electricity, the fibers can also serve as self‐powered tactile and biomechanical sensors. The fibers consist of hollow elastomeric fibers filled with liquid metal. The fibers harvest energy by the combination of triboelectricity (160 V m−1, 5 µA m−1, and ≈360 µW m−1) and induced electrification of the liquid metal (±8 V m−1 (60 Hz), ±1.4 µA m−1, and ≈8 µW m−1). The fibers are characterized and their utility for powering electronics and sensing biomechanical information is demonstrated. These fibers are further demonstrated as completely soft and stretchable components for human–machine interfaces, including keypads and wireless music controllers. Inherently stretchable (>650%) and elastic multifunctional liquid‐metal fibers that can scavenge biomechanical and electromagnetic energy are developed as wearable power providers and self‐powered sensors. These findings optimally unify mechanical freedom and the capability of collecting multiple forms of ambient energy and self‐powered sensing in a single fiber, opening new doors for wearable/stretchable energy and sensing technologies.