The sensitivity of trajectories over finite-time intervals t to perturbations of the initial conditions can be associated with a finite-time Lyapunov exponent λ, obtained from the elements Mij of the stability matrix M. For globally chaotic dynamics, λ tends to a unique value (the usual Lyapunov exponent λ�) for almost all trajectories as t is sent to infinity, but for finite t it depends on the initial conditions of the trajectory and can be considered as a statistical quantity. We compute for a particle moving in a randomly time-dependent, one-dimensional potential how the distribution function P(λ;t) approaches the limiting distribution P(λ;�)=δ(λ-λ�). Our method also applies to the tail of the distribution, which determines the growth rates of moments of Mij. The results are also applicable to the problem of wave-function localization in a disordered one-dimensional potential.