context: In conclusion, a new synthesis approach is presented wherein doped La2Zr2O7 pyrochlore nanocrystals are synthesized with a composition that will result in the correct stoichiometry to form Li-conducting garnets based on Li7La3Zr2O12. La and Ta co-doped pyrochlores with a La:Zr:Ta stoichiometry of 3:1.4:0.6 are demonstrated to readily form garnet-type Li6.4La3Zr1.4Ta0.6O12 between 400–550 °C in a ternary mixture of molten LiNO3–LiOH–Li2O2, with unprecedentedly low reaction temperatures. Pyrochlores can also be used as quasi-single-source precursors and blended with a Li source and reactively sintered in 2 hours at 1200 °C to form highly dense, highly conducting garnet ceramics with a microstructure similar to that obtained through advanced sintering techniques, providing a unique and successful approach to dense garnet electrolytes that can be easily extended to more advanced ceramic forming techniques such as tape-casting or additive manufacturing, potentially improving processability of garnet solid-electrolytes for solid-state lithium batteries.