Untethered twist fibers do not require end‐anchoring structures to hold their twist orientation and offer simple designs and convenient operation. The reversible responsiveness of these fibers allows them to generate torque and rotational deformation continuously upon the application of external stimuli. The fibers therefore have potential in rotating microengines. In practical applications, high torque and rotational deformation are desirable to meet work capacity requirements. However, the simultaneous endowment of reversible responsiveness and high rotational performance to untethered twist fibers remains a challenge. In this study, a liquid crystal elastomer twist fiber (LCETF) is designed and developed with a fixed twisting alignment of mesogens to provide untethered and reversible responsiveness. Outstanding rotational performance can be achieved when the mesogenic orientation is disrupted through heat triggering. Owing to the significant intrinsic contractile ratio of the LCE material, the rotational deformation of the LCETF can reach 243.6° mm−1. More importantly, the specific torque can reach 10.1 N m kg−1, which exceeds previously reported values. In addition, the LCETF can be exploited in a rotating microengine to convert heat into electricity with an induction voltage as high as 9.4 V. This work broadens the applications of LCEs for energy harvesters, micromachines, and soft robots. Untethered twist fibers with reversible responsiveness have shown great potential as rotating microengine, of which high torque and high rotational deformation are desirable. Herein, liquid crystal elastomer twist fiber (LCETF) with fixed twisting orientation is developed, demonstrating outstanding rotational performance due to its significant intrinsic deformation. The obtained LCETF can function as a rotating microengine in an electricity generator.