  We establish a closed formula for a singular vector of weight $\lambda-\beta$
in the Verma module of highest weight $\lambda$ for Lie superalgebra
$\mathfrak{gl}(m|n)$ when $\lambda$ is atypical with respect to an odd positive
root $\beta$. It is further shown that this vector is unique up to a scalar
multiple, and it descends to a singular vector, again unique up to a scalar
multiple, in the corresponding Kac module when both $\lambda$ and
$\lambda-\beta$ are dominant integral.
