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 ~1907 nm. Lasing characteristics of a 1.5 at.% and a 2.0 at.% Ho³⁺-doped YAG ceramic were investigated and compared. Using an output coupler of 6% transmission, over 21.4 W of cw output power at 2097 nm has been generated with the 1.5 at.% doped Ho:YAG ceramic under 35 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%.