5’ cap modification is important for the function of mRNA vaccines and therapeutics, and Vaccinia virus RNA capping enzyme (VCE) has been successfully used in large-scale synthetic mRNA cap incorporation. Here we present the characterization of a novel mRNA capping enzyme derived from Faustovirus, a giant virus that is known to infect Vermamoeba. Faustovirus mRNA capping enzyme (FCE) is a single-chain enzyme that carries all three enzymatic activities necessary to generate the 5’ Cap-0 structure on in vitro transcripts efficiently. Compared to VCE, FCE exhibits higher specific activity on most in vitro transcripts and is more efficient in capping RNA containing certain 5’ secondary structures. FCE is highly active over a broad range of reaction temperatures (25-50°C) and is compatible with Vaccinia virus cap 2’O methyltransferase for one-step generation of the Cap-1 structure on in vitro transcripts. Our findings showed that FCE is a robust RNA capping enzyme suitable for large scale mRNA capping applications.