Williams, who gave birth in September, advanced to the Wimbledon fourth round with a win over Kristina Mladenovic on Friday.
And just hours later, the 36-year-old said she had been in training when Olympia took her first steps.
"She took her first steps... I was training and missed it. I cried," Williams wrote on Twitter.
The American star last week posted on the Olympia's Instagram account showing her on one of Wimbledon's grass courts.
Williams was asked at Wimbledon why she has given her daughter such a public profile, given some fellow players keep their families out of the spotlight.
"I mean, it's 2018. I'm so modern," Williams said.
"For me, it was so natural. She's so fun. I just want to share those moments with everyone.
"We don't share a lot on her page, but we do share enough. It's just so cool." Williams, chasing a 24th Grand Slam title, faces Russian qualifier Evgeniya Rodina in the last 16 on Monday.
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