We present Giant Meterwave Radio Telescope ( GMRT ) and Westerbork Synthesis Radio Telescope ( WSRT ) observations of the recently discovered Local Group dwarf galaxy , Leo T. The peak H i column density is measured to be 7 \times 10 ^ { 20 } cm ^ { -2 } , and the total H i mass is 2.8 \times 10 ^ { 5 } M _ { \odot } , based on a distance of 420 kpc . Leo T has both cold ( \sim 500 K ) and warm ( \sim 6000 K ) H i at its core , with a global velocity dispersion of 6.9 km s ^ { -1 } , from which we derive a dynamical mass within the H i radius of 3.3 \times 10 ^ { 6 } M _ { \odot } , and a mass-to-light ratio of greater than 50 . We calculate the Jeans mass from the radial profiles of the H i column density and velocity dispersion , and predict that the gas should be globally stable against star formation . This finding is inconsistent with the half light radius of Leo T , which extends to 170 pc , and indicates that local conditions must determine where star formation takes place . Leo T is not only the lowest luminosity galaxy with on-going star formation discovered to date , it is also the most dark matter dominated , gas-rich dwarf in the Local Group .