Alexis Olympia Ohanian Jr. appeared a little shy as Williams carried her down the catwalk after unveiling her spring and summer collection to a star-studded audience that included Kim Kardashian and model Ashley Graham.
The S by Serena collection launched in 2018 and comprises a range of size-inclusive pieces. It has been designed for women who "break traditions and boundaries" and "unconquerable mothers, daughters and sisters," according to the website.
To mark Olympia's second birthday on September 1, Williams shared a photo of her as a newborn on Instagram, with the caption: "The last 2 years have been my greatest accomplishment."
On Saturday, the 37-year-old lost out on the US Open women's final to rival Bianca Andreescu, who beat her 6-3, 7-5. Williams, who has 23 Grand Slam wins to her name, won her first US Open title in 1999.
The sport star revealed earlier this year that she was pregnant when she won her 23rd Grand Slam title in 2017.