A high conversion efficiency microwave photonic frequency downconverter based on an integrated dual-parallel Mach Zehnder modulator (DPMZM) and optical phase shifter configuration, is presented. This structure features the advantages of high conversion efficiency, robust operation, and ability to function over a very wide frequency range. The introduction of a novel phase shifter that is incorporated within the structure enables a high rejection of over 45 dB of the local oscillator (LO) to be achieved. The integrated DPMZM based photonic mixer also has a lower noise figure and a higher spurious free dynamic range compared to the conventional dual-series modulator based photonic mixer. Experimental results demonstrate a significant improvement of 23.7 dB in the conversion efficiency compared to the conventional dual-series modulator based photonic mixer for the same optical power into the photodetector.