  Uniaxial stress, as well as hydrostatic pressure are often used to tune
material properties in condensed matter physics. Here, we present a setup which
allows for the study of the combined effects of quasi-uniaxial stress and
hydrostatic pressure. Following earlier designs for measurements under finite
stress at ambient pressure (e.g., Chu et al., Science 337, 710 (2012)), the
present setup utilizes a piezoelectric actuator to change stress in situ inside
the piston-cylinder pressure cell. We show that the actuator can be operated
over the full temperature (from 30K up to 260 K) and pressure range (up to
~2GPa), resulting in a clear and measurable quasi-uniaxial strain. To
demonstrate functionality, measurements of the elastoresistance (i.e., the
change of resistance of a sample as a response to quasi-uniaxial strain) under
finite hydrostatic pressure on the iron-based compound BaFe$_2$As$_2$ are
presented as a proof-of-principle example, and discussed in the framework of
electronic nematicity. Overall, this work introduces the combination of in situ
tunable quasi-uniaxial stress and large (up to ~2GPa) hydrostatic pressure as a
powerful combination in the study of novel electronic phases. In addition, it
also points towards further technical advancements which can be made in the
future.
