Catalyzes the reversible transfer of acyl groups from carnitine to coenzyme A (CoA) and regulates the acyl-CoA/CoA ratio. Also plays a crucial role in the transport of fatty acids for beta- oxidation (PubMed:15099582, PubMed:29395073). Responsible for the synthesis of short- and branched-chain acylcarnitines (PubMed:23485643). Active towards some branched-chain amino acid oxidation pathway (BCAAO) intermediates (PubMed:23485643). Trans-2- enoyl-CoAs and 2-methylacyl-CoAs are poor substrates (PubMed:23485643). {ECO:0000269|PubMed:15099582, ECO:0000269|PubMed:23485643, ECO:0000269|PubMed:29395073}. This is the function of CRAT (carnitine O-acetyltransferase, Ensembl gene identifier ENSG00000095321).