In this paper, we derive a comparison principle for non-negative weak sub- and super-solutions to doubly nonlinear parabolic partial differential equations whose prototype is ∂ t u q - div ( | ∇ u | p - 2 ∇ u ) = 0 in Ω T , with q > 0 and p > 1 and Ω T : = Ω × ( 0 , T ) ⊂ R n + 1 . Instead of requiring a lower bound for the sub- or super-solutions in the whole domain Ω T , we only assume the lateral boundary data to be strictly positive. The main results yield some applications. Firstly, we obtain uniqueness of non-negative weak solutions to the associated Cauchy-Dirichlet problem. Secondly, we prove that any weak solution is also a viscosity solution.