“There comes a time in life when we have to decide to move in a different direction,” the 40-year-old, 23-time Grand Slam winner said in a post on Instagram.
“That time is always hard when you love something so much. My goodness do I enjoy tennis. But now, the countdown has begun.
“I have to focus on being a mom, my spiritual goals and finally discovering a different, but just exciting Serena. I’m gonna relish these next few weeks.”
Williams won the last of her 23 Slams at the 2017 Australian Open when she was already pregnant with daughter, Olympia.
However, she has failed to add a 24th major which would take her level with Margaret Court’s all-time record.
Her final attempt will come at the US Open in New York later this month.
Williams stepped onto a hardcourt for the first time in a year and a half on Monday in the WTA Toronto tournament where fought through to the second round with a straight sets victory over Nuria Parrizas Diaz.
It was her first singles victory since the 2021 French Open, some 14 months ago.
The former world number one had played her first singles match in a year during a first round defeat at Wimbledon in June.