In this paper, we present the development of a widely tunable dual-wavelength fiber laser, which is based on a polarization maintaining thulium-doped fiber and Volume Bragg Gratings (VBGs) triggering the emission wavelengths in the 2 μm band. A wavelength separation range (Δλ) continuously tunable from 1 nm to 144 nm (0.08-11.47 THz) is demonstrated, with > 4.5 W of output power over the tuning range. The laser emission exhibits a linewidth (FWHM) lower than 0.1 nm independent from wavelengths and Δλ, with a signal over noise contrast higher than 45 dB. A maximum output power of 7 W is obtained for shorter Δλ (1-14 nm), corresponding to a slope efficiency of 33% with respect to the incident pump power at 790 nm.