The 23-time grand slam winner has been absent from the Tour since the 2017 Australian Open, which she won despite being in the early stages of pregnancy.
Williams gave birth to her daughter in September, and is preparing to make her comeback at the Indian Wells Masters on Thursday against Zarina Diyas.
Her first-round match coincides with International Women's Day, so the 36-year-old is planning to wear a special accessory to mark the occasion.
"It's official. My comeback is here. This Thursday I will start playing tennis again professionally for the first time since giving birth to my daughter," Williams posted on Instagram.
"This whole month I am playing tournaments in California and Florida - both my home states. Thursday, the day I play my very first match, marks International Women's Day.
"My comeback could not have come on a better day and I decided I wanted to do something different let you all be a part of my long journey back (if you want of course!!) So I created my Serena Gold toned 'S' pin."
Williams went on to explain that the pin is a sign of support for her charity.
"They are for now only available for my fans that come see me at Indian Wells and Miami starting Wednesday as well as Thursday when I play!! Sooooo if you are watching me stop by the Serena booth to grab a 'S' pin," she continued.
"Post pics of you wearing your 'S' and tag me! Thanks for the support I look forward to seeing you out there!!"