Despite the tremendous success of the Standard Model (SM), it needs to be extended to explain the origin of cosmological inflation, dark matter (DM) and neutrino masses. We consider gauged U(1)x extended SM, where in addition to the SM particles, the model includes a U(1)x scalar, Z' gauge boson, and three generations of right-handed neutrinos (RHNs), where the U(1)x charges of all the particles are defined by a single free parameter xH. In this model context, we discuss the complementarity between the cosmological inflation, the DM physics, and new physics searches at the Large Hadron Colliders (LHC). With the identification of the U(1)x scalar as an inflaton field, we consider the cosmological inflation scenario. For an effective inflaton potential to develop an inflection-point with predictions consistent with cosmological observations, the mass ratios among the Z' boson, the RHNs, and the inflaton are fixed. Requiring the inflationary prediction to be consistent with the current cosmological observation and collider experimental results, we show that our scenario can be tested at the future collider experiments such as the High Luminosity-LHC and the SHiP experiment. We also consider SU(5) x U(1)x scenario, where the SU(5) grand unification of the SM quarks and leptons is realized for xH = -4/5. Hence, the U(1)x charge is quantized in this scenario. With an additional global Z-2 symmetry, one RHN, which is Z-2 odd particles, serves as the DM in the universe. We investigate the Z'-portal RHN DM scenario and find that the constraints from the DM relic abundance and the search results for a Z' boson resonance at the LHC Run-2 are complementary to narrow down the allowed parameter region, which will be fully covered by the future LHC experiments for the Z’ boson mass less than 5 TeV.