We present a transistor-based microwave metamaterial exhibiting tunability over a wide range of time scales. By loading a metamaterial with a transistor, we show through theory and simulation that both the resonant frequency and quality factor of the metamaterial can be dynamically tuned with a voltage bias. We demonstrate through experiment that such a time-varying transistor-based metamaterial exhibits this tunability. The tunability is applicable to a wide range of time scales, from quasi-static effective parameter tuning to parametric pumping for mixing and phase conjugation. We then apply the metamaterial to a particular application of phase conjugation and demonstrate through simulation and experiment that a very strong phase conjugated signal is produced. We experimentally show that the mixing efficiency for a transistor metamaterial is over 30 dB stronger than that of a varactor-based phase conjugate metamaterial. © 2014 AIP Publishing LLC.