In this paper, the absorption and fluorescence spectra of ${\mathrm{Er}}^3$, ${\mathrm{Pr}}^3$ co-doped ${\mathrm{LiYF}}_4$ (Er,Pr:YLF) crystal were measured and analyzed. The ${\mathrm{Pr}}^3$ co-doping was proved to effectively enhance the ${\mathrm{Er}}^3:{{}^4\mathrm{I}}_{11/2}\to {{}^4\mathrm{I}}_{13/2}$ mid-infrared transition at the 2.7 μm with 74.1% energy transfer efficiency from ${\mathrm{Er}}^3:{{}^4\mathrm{I}}_{13/2}$ to ${\mathrm{Pr}}^3:{{}^3\mathrm{F}}_4$. By using the Judd–Ofelt theory, the stimulated emission cross section was calculated to be $1.834\times {10}^{-20}{\mathrm{cm}}^2$ at 2685 nm and $1.359\times {10}^{-20}{\mathrm{cm}}^2$ at 2804.6 nm. Moreover, a diode-end-pumped Er,Pr:YLF laser operating at 2659 nm was realized for the first time, to the best of our knowledge. The maximum output power was determined to be 258 mW with a slope efficiency of 7.4%, and the corresponding beam quality factors ${\mathit{M}}_{\mathit{x}}^2=1.29$ and ${\mathit{M}}_{\mathit{y}}^2=1.25$. Our results suggest that Er,Pr:YLF should be a promising material for 2.7 μm laser generation.