  We compute mixed QCD-electroweak corrections to the fully-differential
production of an on-shell $W$ boson. Decays of $W$ bosons to lepton pairs are
included in the leading order approximation. The required two-loop virtual
corrections are computed analytically for arbitrary values of the electroweak
gauge boson masses. Analytic results for integrated subtraction terms are
obtained within a soft-collinear subtraction scheme optimized to accommodate
the structural simplicity of infra-red singularities of mixed QCD-electroweak
contributions. Numerical results for mixed corrections to the fiducial cross
section of $pp \to W^+ \to l^+ \nu$ and selected kinematic distributions in
this process are presented.
