For a double-pass-pumped cw Tm:YAG laser, we developed a theoretical model, taking into account reabsorption loss and mode matching between the pumping light and the cavity mode. We also demonstrated that efficient operation can be obtained with a simple cavity configuration by using a dichroic output mirror, highly reflective at the pumping wavelength and partially reflective at the lasing wavelength. Experimental comparisons of this pumping method with single-pass pumping showed that the longitudinally double-pass-pumped Tm:YAG laser performs as well at room temperature as the single-pass-pumped laser performs at -10 degrees C.