Effect of pressure on the transport properties and thermoelectric performance of Dirac semimetal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>ZrTe</mml:mi> <mml:mn>5</mml:mn> </mml:msub> </mml:math>

${\mathrm{ZrTe}}_{5}$ has been extensively studied because of its novel topological properties, which are tunable by subjecting to various parameters like temperature, chemical synthesis conditions, and pressure. In this study, we have investigated and compared the effect of hydrostatic pressure up to \ensuremath{\sim}20 kbar on the transport properties of ${\mathrm{ZrTe}}_{5}$ single crystals grown by chemical vapor transport (CVT) and flux methods. With the application of pressure, the electrical resistivity $\ensuremath{\rho}(T)$ and thermopower $S(T)$ of both crystals were found to increase in the whole temperature range unlike the other known thermoelectric materials, such as ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$, SnSe etc. This observation is supported by complementary first-principles band-structure calculations, as the application of pressure widens the direct band gap at $\mathrm{\ensuremath{\Gamma}}$ point. Moreover, the analysis of the pressure-dependent magnetotransport and Shubnikov-de Hass oscillation results revealed an increase in carrier concentration and effective mass along with reduction of mobility as pressure rises. Furthermore, with the application of pressure, the flux-grown ${\mathrm{ZrTe}}_{5}$ crystals display a transition from unipolar to bipolar charge transport as evidenced by the emergence of a resistivity peak at ${T}^{*}$ under high pressure, unlike the CVT-grown ${\mathrm{ZrTe}}_{5}$ crystals where the bipolar charge transport near its characteristic resistivity peak $({T}_{\mathrm{p}})$ remains unaffected. Our study also reveals a pressure-induced enhancement of ${T}_{\mathrm{p}}$ and ${T}^{*}$ for both crystals, suggesting an upward shift of the Fermi level upon compression. Additionally, for the CVT-grown ${\mathrm{ZrTe}}_{5}$ crystals, the application of pressure nearly doubled the thermoelectric power factor (PF) at 18.2 kbar and room temperature. In contrast, for the flux-grown ${\mathrm{ZrTe}}_{5}$ crystals, the PF varies weakly as the pressure is raised to 17 kbar. Our results underscore the role of crystal synthesis technique along with the application of pressure as an effective strategy to optimize the magnetotransport and thermoelectric performance of ${\mathrm{ZrTe}}_{5}$.