  In this thesis, major developments in the publicly available program SecDec
are presented, extending the numerical evaluation of multi-loop multi-scale
integrals from Euclidean to physical kinematics. The power of this new feature
is shown in two phenomenological applications. In the first, numerical results
for several massive two-loop four-point functions are shown. In its second
application within this thesis, the leading momentum-dependent two-loop
corrections to the neutral $\mathcal{CP}$-even MSSM Higgs-boson masses are
calculated. The results are included in the code FeynHiggs.
