<p>Soil alkalization severely restricts alfalfa (<i>Medicago sativa</i> L.) productivity by disrupting ion homeostasis and impairing photosynthetic system function. To elucidate the role of Shaker-type K⁺ channels in alfalfa under NaHCO₃-induced alkali stress, we identified seven Shaker-type K⁺ channel genes in the ‘Zhongmu No. 1’ genome. These genes belong to five conserved subfamilies and contain promoter cis-elements associated with hormone signaling and stress responsiveness. Reanalysis of a previously published transcriptome dataset revealed coordinated expression changes in Shaker-type K⁺ channel genes and several representative K⁺ transport-related genes under NaHCO₃ treatment (0, 100, 200, and 300 mM). Among the Shaker family members, <i>MsSKOR</i> showed the strongest and most sustained induction across stress gradients, suggesting a central role in K⁺ translocation during alkali stress. Functional assays further demonstrated that <i>MsSKOR</i>-overexpressing tobacco exhibited markedly enhanced tolerance to NaHCO₃-induced alkali stress, including higher leaf K⁺ content, reduced sodium ions (Na⁺) accumulation, and a sustained high K⁺/Na⁺ ratio. Overexpression lines also showed alleviated wilting, decreased reactive oxygen species (ROS) accumulation, and reduced malondialdehyde (MDA) and proline (Pro) levels, indicating improved membrane stability and antioxidant capacity. In addition, the transgenic plants maintained more stable chlorophyll fluorescence transients and PSI-related signals under stress, indicating improved protection of the photosynthetic apparatus. Collectively, our findings demonstrate that <i>MsSKOR</i> enhances K⁺ homeostasis and maintains K⁺/Na⁺ balance, thereby mitigating oxidative damage and stabilizing photosynthetic performance under NaHCO₃-induced alkali stress. These results identify <i>MsSKOR</i> as a positive regulator of alkali stress tolerance and a promising candidate gene for the genetic improvement of alfalfa cultivated on saline-alkaline soils.</p>