The structure and thermoelectric (TE) properties of La-doped, A-site deficient SrTiO3 (Sr1-3x/2LaxTiO3) ceramics sintered in air and N2/5%H2 have been investigated. Air sintered ceramics with 0.10 ≤ x < 0.30 appear cubic by X-ray diffraction (XRD) but exhibit superstructure consistent with a tetragonal cell (a0a0c-), according to electron diffraction (ED) studies. 0.30 ≤ x < 0.50 have additional short range A-site vacancy (VA) ordering and x ≥ 0.50 are orthorhombic with an a-a-c+ tilt system and long range VA ordering. 0.10 ≤ x ≤ 0.50 reduced in N2/5%H2 are oxygen-deficient and appear cubic in XRD patterns but exhibit superstructure compliant with an a0a0c- tilt system by ED. For x = 0.50, additional short range VA order is observed and x > 0.50 are orthorhombic with an a-a-c+ tilt system and long range VA ordering. x = 0.15 sintered in N2/5%H2 show the largest dimensionless TE figure-of-merit ZT = 0.41 at 973 K reported for n-type SrTiO3-based ceramics, suggesting the accommodation of La through formation of VSr coupled with reduction in N2/5%H2 represents a new protocol for the development of oxide-based thermoelectrics.