The paper presents a significant advancement in the field of optical quantum computing and communications by demonstrating giant polarization rotations induced by a single electron spin in a cavity-enhanced spin-photon interface. The study uses an electrically contacted pillar-based cavity embedding a single InGaAs quantum dot to achieve these rotations. A complete tomography approach is introduced to extrapolate the output polarization Stokes vector, conditioned by a specific spin state, in the presence of spin and charge fluctuations. The experimental results show that the device can approach polarization states conditionally rotated by $\pi/2$, $\pi$, and $-\pi/2$ in the Poincaré sphere with fidelities of $(97 \pm 1)\%$, $(84 \pm 7)\%$, and $(90 \pm 8)\%$, respectively. The enhanced light-matter coupling, limited cavity birefringence, and reduced spectral fluctuations enable targeting most conditional rotations in the Poincaré sphere with both longitudinal and latitudinal control. This work highlights the potential of such interfaces for various configurations and protocols in quantum information processing.The paper presents a significant advancement in the field of optical quantum computing and communications by demonstrating giant polarization rotations induced by a single electron spin in a cavity-enhanced spin-photon interface. The study uses an electrically contacted pillar-based cavity embedding a single InGaAs quantum dot to achieve these rotations. A complete tomography approach is introduced to extrapolate the output polarization Stokes vector, conditioned by a specific spin state, in the presence of spin and charge fluctuations. The experimental results show that the device can approach polarization states conditionally rotated by $\pi/2$, $\pi$, and $-\pi/2$ in the Poincaré sphere with fidelities of $(97 \pm 1)\%$, $(84 \pm 7)\%$, and $(90 \pm 8)\%$, respectively. The enhanced light-matter coupling, limited cavity birefringence, and reduced spectral fluctuations enable targeting most conditional rotations in the Poincaré sphere with both longitudinal and latitudinal control. This work highlights the potential of such interfaces for various configurations and protocols in quantum information processing.