We report on the high-power and high-efficiency operation of a polycrystalline Ho:YAG ceramic laser in-band pumped by a Tm fiber laser at $\sim 1907\mathrm{nm}$ . Lasing characteristics of a $1.5\text{\hspace{0.17em} at.}\%$ and a $2.0\text{\hspace{0.17em} at.}\%$ ${\mathrm{Ho}}^{3+}$ -doped YAG ceramic were investigated and compared. Using an output coupler of 6% transmission, over $21.4\mathrm{W}$ of cw output power at $2097\mathrm{nm}$ has been generated with the $1.5\text{\hspace{0.17em} at.}\%$ doped Ho:YAG ceramic under $35\mathrm{W}$ of incident pump power, corresponding to an average slope efficiency with respect to the incident pump power of 63.6% and an optical-to-optical conversion efficiency of 61.1%.