In the depths of ice giant planets such as Neptune and Uranus, and in the inertial confinement fusion targets, chemical reactions can be significantly affected by the extreme pressure and temperature conditions. One of the most intriguing phenomena is the possible formation of diamond from hydrocarbon fluids. Despite some experimental observations of diamonds being formed, its mechanism from first principles, i.e., density functional theory (DFT) perspective has not been well understood. In this work, we provide evidence of diamond survival and possible growth using large-scale DFT-based and machine learned molecular dynamics (MD) simulations. Our large-scale MD based ‘reverse strategy’ model, involving the mixing of stable phases of individual elements, indicate that diamond can indeed survive with hydrogen atoms outside, at extreme pressure and temperatures relevant to ice giant mantles. The time evolution of these MD simulations depict the 26 mechanism of survival and eventual growth of diamond surrounded with hydrogen atoms and CH fluid. Our transport calculations based on Kubo–Greenwood formalism reveal that the diamond28 hydrogen system has lower electrical and thermal conductivity than complete hydrocarbon fluid at 150 GPa and 3000 - 4000 K. We expect these results to have important impacts in the modeling of the structure and magnetic fields of the ice giant planet interiors and improve future inertial fusion energy target designs.