Methionyl-tRNA formyltransferase that formylates methionyl-tRNA in mitochondria and is crucial for translation initiation. (6S)-10-formyltetrahydrofolate + L-methionyl-tRNA(fMet) = (6S)-5,6,7,8-tetrahydrofolate + H(+) + N-formyl-L-methionyl-tRNA(fMet) Composed of an N- and a C-terminal domain. The N-terminal domain carries the tetrahydrofolate (THF)-binding site and the C-terminal domain is presumably involved in positioning the Met-tRNA substrate for the formylation reaction. Belongs to the Fmt family.