We have demonstrated what we believe to be the first mid-infrared optical parametric oscillator (OPO) pumped directly by a pulsed Tm-doped fiber laser. The Tm-fiber pump laser produces $30\mathrm{ns}$ pulses with a repetition rate of $30\mathrm{kHz}$ at a wavelength of $2\mu \mathrm{m}$ . The $\mathrm{Zn}\mathrm{Ge}{\mathrm{P}}_2$ (ZGP) OPO produces $20\mathrm{ns}$ mid-IR pulses in the $3.4–3.9\mu \mathrm{m}$ and $4.1–4.7\mu \mathrm{m}$ spectral regions simultaneously. More than $658\mathrm{mW}$ of mid-IR output power has been generated with a total OPO slope efficiency greater than 35%.