Laser intensity noise suppression in the millihertz frequency band is essential for space-based gravitational wave detection to ensure the sensitivity of the interferometer. Photonic feedback technology is one of the most effective methods for suppressing laser intensity noise. As the first-stage component in the feedback loop, the noise of the photodetector directly couples into the feedback loop, significantly impacting the laser intensity noise. Starting from the requirement to suppress laser intensity noise in the 0.1 mHz-1 Hz frequency band for space-based gravitational wave detection, this paper provides a detailed analysis of the factors influencing the electronics of photodetectors at extremely low frequencies. Leveraging the low dark current characteristic of photodiodes in photovoltaic mode, a zero-bias voltage scheme is adopted to reduce the dark noise of the photodiode. A transimpedance amplification circuit is designed using an integrated operational amplifier with zero offset voltage drift and low-temperature drift metal foil resistors, optimizing the transimpedance capacitor and follower circuit to reduce 1/f noise in the circuit. Active temperature control is employed to stabilize the photodiode's responsivity, and additional measures such as using a self-developed low-noise power supply and shielding against interference are implemented to further reduce noise. Ultimately, an ultra-low electronic noise photodetector operating in the 0.1 mHz-1 Hz frequency band is developed. A self-developed intensity noise evaluation system is used to comprehensively assess the noise in both the time and frequency domains, and experimental results demonstrate the constant noise characteristics of the developed detector. The experimental results show that the electronic noise spectral density of the developed detector reaches 2×10^-6V/Hz^1/2 in the 0.1 mHz-1 Hz frequency band, and the detector's electronic noise does not vary with optical power. The detector achieves a gain of 35 kV/W at 1064 nm. The noise performance of the detector is two orders of magnitude lower than the laser intensity noise requirement (10^-4/Hz^1/2) for space-based gravitational wave detection, providing a critical component and technical support for high-gain photonic feedback control and laser intensity noise suppression in space-based gravitational wave detection.