Catalyzes the attachment of threonine to tRNA(Thr) in a two- step reaction: threonine is first activated by ATP to form Thr-AMP and then transferred to the acceptor end of tRNA(Thr). Also edits incorrectly charged tRNA(Thr) via its editing domain. . This is the function of Ensembl gene identifier ENSG00000143374 (TARS2, threonyl-tRNA synthetase 2, mitochondrial).