A liquid-crystal tunable fishnet metamaterial is designed and investigated for use in the terahertz spectrum. A nematic material layer is introduced between the two fishnet metallic structures. Tuning of the nematic molecular orientation is shown to shift the magnetic resonance frequency of the metamaterial and its electromagnetic properties. A shift of 100 GHz is demonstrated for common dielectric and liquid-crystalline materials used in terahertz technology. The response time of the tunable metamaterial is in the millisecond range, orders of magnitude lower than in thus far demonstrated liquid-crystal based terahertz components.