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Zero-intermediate frequency (IF) receiver features the advantages of compact structure and agile operating frequency, but faces the problems of local oscillator (LO) leakage, direct current (dc) offset, even-order distortion, and in-phase/quadrature (I/Q) imbalance. In this paper, a photonic microwave I/Q mixer for zero-IF receiver is proposed based on a single integrated polarization multiplexing Mach–Zehnder modulator (PDM-MZM). Thanks to its all-optical operation and LO power optimization, an I/Q phase imbalance below 0.9°, an isolation ratio below −30 dB, and a typical conversion gain of −2.3 dB are achieved over an ultra-wide operating frequency from 10 to 40 GHz. Combined with the balanced detection techniques, the dc offset and even-order distortions are well suppressed, and the typical third-order spurious free dynamic range is 107.9 dB $\cdot $ Hz ^{2/3} . Using the proposed photonic I/Q mixer, the vector signals with various modulation formats, carrier frequencies, and data rates (200–700 Mb/s) are directly demodulated to I/Q basebands, and the error vector magnitude and the bit rate error are measured with the power range from −25 to 15 dBm. Subharmonic vector I/Q demodulation is also experimentally demonstrated. The proposed all-optical, ultra-wideband and high-efficient microwave I/Q mixer is suitable for a zero-IF receiver and may find potential applications in electronic systems such as wideband wireless communications, frequency-hopping radar, or multiband satellite transponder. [ABSTRACT FROM PUBLISHER]