The parametric coupling of electromagnetic and mechanical degrees of freedom gives rise to a host of optomechanical phenomena. Examples include quantum-limited displacement measurements, sideband cooling or amplification of mechanical motion. Likewise, this interaction provides mechanically mediated functionality for the processing of electromagnetic signals, such as microwave amplification. Here, we couple a superconducting niobium coplanar waveguide cavity to a nanomechanical oscillator, and demonstrate all-microwave field-controlled tunable slowing and advancing of microwave signals, with millisecond distortion-free delay and negligible losses. This is realized by using electromechanically induced transparency, an effect analogous to electromagnetically induced transparency in atomic physics. Moreover, by temporally modulating the electromechanical coupling and correspondingly the transparency window, switching of microwave signals is demonstrated and its temporal dynamics investigated. The exquisite temporal control gained over the electromechanical coupling provides the basis for realizing advanced protocols for storage of both classical and quantum microwave signals. © 2013 Macmillan Publishers Limited. All rights reserved.