Catalyzes the specific attachment of L-methionine to its cognate tRNA in a 2 step reaction: the amino acid (AA) is first activated by ATP to form AA-AMP and then transferred to the acceptor end of the tRNA (PubMed:11714285, PubMed:33909043). Plays a role in the synthesis of ribosomal RNA in the nucleolus (PubMed:10791971). In addition, can prevent the misincorporation of homocysteine into tRNA and protein by catalyzing a tRNA-independent hydrolysis of the misactivated homocysteinyl-AMP intermediate. The homocysteinyl-AMP intermediate undergoes an intramolecular cyclization reaction in which the thiolate side chain of homocysteine displaces the AMP group, forming homocysteine-thiolactone and AMP (By similarity). {ECO:0000250|UniProtKB:A0A9J7F5X6, ECO:0000269|PubMed:10791971, ECO:0000269|PubMed:11714285, ECO:0000269|PubMed:33909043}. This is the function of ENSG00000166986 (MARS1, methionyl-tRNA synthetase 1).