A $6.4\mathrm{at.}\%$ ${\mathrm{Tm}}^{3+}$ -doped $\mathrm{Ba}{\mathrm{Gd}}_2{\left(\mathrm{Mo}{\mathrm{O}}_4\right)}_4$ cleavage crystal was grown by the Czochralski method. Detailed spectral properties of this crystal were investigated, including the polarized absorption and emission spectra and the fluorescence decay. The maximum absorption cross section of the pump band is $3.5\mathrm{cm}\times {10}^{-20}\mathrm{cm}$ at $798\mathrm{nm}$ with a bandwidth of $8\mathrm{nm}$ , which means that this crystal is suitable for laser diode pumping. The Judd–Ofelt theory was used to calculate the radiative transition probabilities between multiplets. Pumped by a Ti:sapphire laser, the $\sim 2.0\mu \mathrm{m}$ quasi-cw laser operation was performed using a cleaved $1.1\mathrm{mm}$ thick wafer of this crystal in a hemispherical cavity. The achieved highest slope efficiency was 51% with a 6.7% output coupler and the corresponding threshold was $31\mathrm{mW}$ . The results show that a ${\mathrm{Tm}}^{3+}:\mathrm{Ba}{\mathrm{Gd}}_2{\left(\mathrm{Mo}{\mathrm{O}}_4\right)}_4$ crystal is a promising candidate for $\sim 2.0\mu \mathrm{m}$ microchip lasers.