The tot, who was born on Saturday, is Kim's second child with husband Kanye West.
She told the world her newborn's name via Twitter, attaching a picture of four emojis to represent her growing family.
Related articles
The baby's moniker has rapidly begun trending on Twitter, with users falling over themselves to comment on the news.
One enthusiast wrote: "Saint West. This calls for a scores update. Kimye: 500 points. Haters: 0. Baby name predictors: -500. Oh my god, I am so happy."
Saint West would be a terrific name for the hero in a 90s action movie
"I hope Saint West, leads a holy life and is converted and becomes Saint Saint West, Patron Saint of College Dropouts," said someone else.
"Saint West would be a terrific name for the hero in a 90s action movie," joked another tweeter.
Another person, taking the opposite approach, posted: "Saint?! Really?? Kim and Kanye are officially not allowed to name anymore humans…"
Others were disappointed with the name, with one person saying: "first North West.... now Saint West...... if Wild West doesn't come soon I'm sueing".
Reality superstar Kim also revealed that Saint's weight was eight pounds and one ounce when he was delivered on December 5.
It was previously reported that his due date was Christmas Day, and she had an operation just last week to turn him around after discovering he was in a breech position.
She gave birth to her first child, North West, in 2013.