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) (PubMed:25824639, PubMed:31374204). Also edits incorrectly charged tRNA(Thr) via its editing domain, at the post-transfer stage (By similarity). {ECO:0000250|UniProtKB:Q9D0R2, ECO:0000269|PubMed:25824639, ECO:0000269|PubMed:31374204}. This is the function of TARS1 (threonyl-tRNA synthetase 1, Ensembl gene identifier ENSG00000113407).