On the basis of experimental results, we propose a new friction law aiming at describing the mechanical behavior of thick gouge layers. As shown in the companion paper, the dominant effect to take into account is a significant slip‐weakening process active over decimetric slip distances. This slip weakening is strongly nonlinear and, formerly, does not involve any characteristic length scale. The decrease of the gouge friction coefficient μ with imposed slip δ is well modeled by a power law: μ = μ0 + αδ−β, with β = 0.4. On this major trend are superimposed second‐order velocity‐weakening and time‐strengthening effects. These effects can be described using classical rate‐ and state‐dependent friction (RSF) laws and are associated with a small length scale dc ≈ 100 μm. Consistent with the general RSF framework, we combine slip‐weakening and second‐order effects in a slip, rate, and state (SRS) friction law with two state variables. We then compute the fracture (or breakdown) energy Gc and the apparent weakening distance Dcapp associated with the slip‐weakening process. Once extrapolated to realistic “geophysical” confining pressures, the obtained values are in excellent agreement with those inferred from real earthquakes: Gc ≈ 5 × 106 J m−2 and Dcapp ≈ 20 cm. We also find that fracture energy scales with imposed slip in our experiments: Gc ∼ δ0.6.