The proposed neutron electric dipole moment (nEDM) experiment to be carried out at the Spallation Neutron Source (SNS) in Oak Ridge National Laboratory (ORNL) will look for the change in the Larmor precession frequencies of the neutron placed in external parallel magnetic and electric fields when the electric field direction is reversed. The frequency measurement will be carried out by monitoring the scintillation light from the n-$^3$He spin-dependent nuclear process in superfluid $^4$He. The polarized $^3$He will also be used as a co-magnetometer to monitor the \emph{in situ} magnetic field during the experiment. Relaxation time measurements of polarized $^{3}$He have been performed under the experimental conditions to ensure that the $^{3}$He polarization have a sufficiently long relaxation time in order for the nEDM experiment to achieve the proposed sensitivity. Polarized $^3$He also finds its application in the three-body photodisintegration differential cross section measurements, which will allow for the test of the state-of-the-art three-body calculations and determination of the Gerasimov-Drell-Hearn (GDH) integral on $^3$He, and double polarized Compton scattering experiment, which has the ability to extract the neutron individual spin polarizabilities for the first time, and provide crucial tests of predictions based on effective field theories, dispersion theories, and lattice QCD calculations. A high-pressure double-cell polarized $^3$He target has been constructed for these measurements in the High Intensity Gamma Source (HI$\gamma$S) at Duke Free Electron Laser Laboratory.