System and method embodiments are provided for null filling of IQ waveform. In an embodiment method, samples below a predetermined threshold are selected from a plurality of samples of an input signal. Amplitude values of a complex null-fill function are then calculated to push amplitudes of the samples below the predetermined threshold to a signal level at the predetermined threshold. The phase values of the complex null-fill function are calculated to push the samples of the input signal in an IQ plane in a defined direction from a point closest to a zero signal value. The resulting complex null-fill function is filtered within a predetermined bandwidth of the input signal, and then added to the input signal to provide a modified input signal for amplification.