We present a theoretical scheme for laser cooling in ${\mathrm{Tm}}^{3+}$-doped oxy-fluoride glass ceramic (GC). ${\mathrm{Tm}}^{3+}$-doped GC has a unique combination of high chemical and mechanical stability related to the oxide glass and low phonon energy of the fluoride nanocrystals, which trap a majority of ${\mathrm{Tm}}^{3+}$ ions. This unique property of GC makes it attractive for a number of applications. The effective embedding of rare-earth ions in the crystalline phase with low phonon energy provides high quantum efficiency for the ${}^3{\mathrm{F}}_4\to {}^3{\mathrm{H}}_6$ transition in the ${\mathrm{Tm}}^{3+}$ ions participating in the cooling cycle.