Display omitted •A new type of tensile artificial muscle is introduced for the first time.•The muscle consists of a torsionally-active fiber that is serially connected to an elastomeric fiber.•Heat induced untwist of one fiber causes coil formation and shortening of the second fiber.•Large contraction strains of more than 10% are demonstrated.•A comprehensive mechanics model is developed that accurately describes the new actuation mechanism. A new concept for tensile artificial muscles is introduced in which the torsional actuation of a twisted polymer fibre drives a twist to writhe conversion in a serially attached elastomeric fibre. Thermally induced torsional rotation of the twisted fibre caused formation of coils in the elastomeric fibre which resulted in overall muscle length contraction. Theoretical predictions of the muscle strain were developed by means of a modified single-helix theory. Experimental tests were conducted to measure the isotonic contraction strains for elastomeric fibres of different diameters and lengths. A good agreement between the measured and calculated results was found. Practical applicability of this muscle is evaluated by using different mechanical loading conditions. Actuation contraction strains as high as 10% were observed with excellent reversibility. Unlike original coiled fibre tensile actuators, these twist-coil artificial muscles did not require any pre-conditioning cycles.