We propose a 2-μm-band high optical signal-to-noise-ratio (OSNR) hybrid compound-resonating-cavity (CRC) single-longitudinal-mode (SLM) thulium-doped fiber laser (TDFL). The hybrid CRC consists of an asymmetric linear compound-four-cavity (AL-CFC) made of three uniform fiber Bragg gratings (FBGs) and two optical couplers (OCs), as well as a dual-coupler-ring (DCR) cavity made of two OCs. Based on the Vernier effect, the AL-CFC can select the SLM from dense longitudinal modes, and the DCR is used as a narrow-band filter to further stabilize the operation of SLM lasing over a long term. A 1567-nm laser diode amplified by a high-power erbium-doped fiber amplifier is used as a pump source. Under a pump power of 2.80 W, a stable SLM laser output is achieved at a center wavelength of 2049.160 nm with an output power of 15.47 mW and an OSNR as high as 75.65 dB. The fluctuations of the wavelength and power are respectively lower than 0.005 nm and 0.85 dB within a measurement time of 200 min. The SLM operation becomes stable within 10 min. The pump threshold and slope efficiency are 1.75 W and 1.43%, respectively. The proposed TDFL has potential for applications in free-space optical communication, laser radar, and optical sensing.