  We study the expectation value of the $\mathrm{T}\overline{\mathrm{T}}$
operator in spacetimes with constant curvature. We define an diffeomorphism
invariant biscalar whose coinciding limit gives the expectation value of the
$\mathrm{T}\overline{\mathrm{T}}$ operator. We show that this biscalar is a
constant in flat spacetime, which reproduces Zamolodchikov's result in 2004.
For spacetimes with non-zero curvature, we show that this is no longer true and
the expectation value of the $\mathrm{T}\overline{\mathrm{T}}$ operator depends
on both the one-point and two-point functions of the stress-energy tensor.
