  We use the functional Renormalisation Group (fRG) to describe the in and out
of equilibrium dynamics of stochastic processes, governed by an overdamped
Langevin equation. Exploiting the connection between Langevin dynamics and
supersymmetric quantum mechanics in imaginary time, we write down
renormalisation flow equations for the effective action, approximated in terms
of the Local Potential Approximation and Wavefunction Renormalisation. We
derive \textit{effective equations of motion} (EEOM) from the effective action
(EA) $\Gamma$ for the average position $\left\langle x\right\rangle$, variance
$\langle \left(x- \langle x \rangle\right)^2\rangle$ and covariance. The fRG
flow equations outlined here provide a concrete way to compute the EA and thus
solve the derived EEOM. The obtained effective potential should determine
directly the exact equilibrium statistics, name the position, the variance, as
well as all higher order cumulants of the equilibrium Boltzmann distribution.
This first paper of a two part series is mostly concerned with setting up the
necessary formalism while in part two we will numerically solve the equations
derived her and assess their validity both in and out of equilibrium.
