Millar, who penned the best-selling graphic novel Superman: Red Son, described the actor as a "great choice" for the lead role in Zack Snyder's reboot.
"So many people been pored over all the years and so many of them close, but wrong," he wrote. "Brandon Routh is actually brilliant and you only have to see Scott Pilgrim to see how impeccable his timing is. But he looked more like Christopher Reeve than Superman.
"Dean Cain, Tom Welling and all the others were completely wrong for the part and the big names mooted were never right either. But I completely buy Cavill in this role. That instinctive gut feeling that I'm looking at a pic of Superman."
The Kick-Ass creator went on to criticise the decision to omit Superman's icon red trunks for the character's redesign, but was complimentary of Snyder's overall take on the Last Son of Krypton.
"I don't even mind the costume. Losing the trunks was pointless, throws the balance of the design off and looks truly, truly HORRIBLE in the comics. But the muted colours work really well, those dark blues and reds really making the pics look very rich and regal.
"I love how this is looking. Cavill was a great choice, but then Snyder has a great eye. Cracking team behind this so I have high hopes."
Man of Steel - which also stars Amy Adams and Michael Shannon - will debut in cinemas on June 14. Watch a trailer for the film below: