The fashion heiress, who was overdue by more than a week, proudly took to Twitter to announce the happy news.
"Hello! Finally #ottohermann!" she wrote, alongside a photo of an adorable knitted jumper with the baby's name stitched on it.
CLICK ON PHOTO FOR GALLERY OF 'OTTO' PICTURES
Margherita, 30, teased her fans with a stream of images of all things Otto-related, but has yet to release the first image of the newborn.
"Evviva Otto! (Credit @Ivobisignano )," she tweeted, next to a print of a black and white cat, followed by another snapshot of the phrase "Welcome Otto" written in the sand on the beach.
The latest update came just two days before the newborn arrived, when Margherita revealed she had broken her wrist. The first-time mother, who is an avid user of Twitter and Instagram, showed her characteristically positive nature on her social media feeds.
"#KeepOnSmiling #BrokenWrist #WhenTheGameGetsToughJustLaugh @eugenioamos spend the last few hours as a twosome #waitingforotto shouldn't take much longer," she wrote.
Margherita has been eagerly cataloguing the lead-up to Otto's birth, who was named after her grandfather and fashion legend Ottavio Missoni who died earlier this year.
The new mother revealed her baby's beautiful nursery with a series of snapshots she posted in August. Margherita shared a photo of a 1950s vintage wooden crib with an adorable blue polka dot canopy, as well as a photo of two pillows embroidered with a "mamma" and "papa" stitching.
While the Missoni family have kept mum on the tragic events that they have gone through this year, including the January disappearance of Vittorio Missoni, CEO of the family's fashion house, followed by the death of Ottavio, Margherita recently opened up about the difficult times.
"It has helped us a lot that there are so many of us and we are so tight," she said, speaking to The Times. "It's easier than if you were having to face it all on your own.
"Of course it was hard for me, especially because I'm pregnant. I've had a very intense pregnancy, with all the things that have happened."