We study diffusion-controlled processes in nonequilibrium steady states, where standard rate theory assumptions break down. Using transition path theory, we generalize the relations between reactive probability fluxes and measures of the rate of the reaction. Stochastic thermodynamics analysis reveals how work constrains the enhancement of rates relative to their equilibrium values. An analytically solvable ion pairing model under a strong electric field illustrates and validates our approach and theory. These findings provide deeper insights into diffusion-controlled reaction dynamics beyond equilibrium.