  An observation is reported of the electroweak production of a W$^+$W$^-$ pair
in association with two jets, with both W bosons decaying leptonically. The
data sample corresponds to an integrated luminosity of 138 fb$^{-1}$ of
proton-proton collisions at $\sqrt{s}$ = 13 TeV, collected by the CMS detector
at the CERN LHC. Events are selected by requiring exactly two opposite-sign
leptons (electrons or muons) and two jets with large pseudorapidity separation
and high dijet invariant mass. Events are categorized based on the flavor of
the final-state leptons. A signal is observed with a significance of 5.6
standard deviations (5.2 expected) with respect to the background-only
hypothesis. The measured fiducial cross section is 10.2 $\pm$ 2.0 fb and this
value is consistent with the standard model prediction of 9.1 $\pm$ 0.6 fb.
