She won her first Grand Slam title at the 2005 US Open.
Clijsters was known as "Aussie Kim" after her relationship with Aussie champion Lleyton Hewitt. The pair were engaged but broke up in 2004.
But Clijsters kept the moniker, feeling she live up to it when she won the 2011 Aussie title.
She announced to her followers on Twitter she was returning to the tour for the first time in seven years.
"I don't feel like I need to prove anything, but I want to challenge myself and I want to be strong again," she said. "Let's see if I can get my body in shape to play tennis at a level where I would like it to be at, that I have in mind of where I would like to get to, and see if it's possible. To see, first of all, if my body is capable of even doing that."
The WTA said that as a former top-ranked player Clijsters can receive unlimited wildcards at its tournaments.
Clijsters' last singles match was in the second round of the 2012 US Open but Clijsters' record speaks for itself.
Having claimed 41 singles titles, Clijsters ranks third among active players, behind only the Williams sisters with Serena on 72 titles and Venus on 49.
Clijsters ranks 14th on the Open Era list.
She also reached the semi-finals of a Grand Slam 16 times and won the 2003 French Open and Wimbledon titles in doubles.
She is one of just six women to be simultaneously World No. 1 in singles and doubles.
Speaking on the WTA Insider podcast, Clijsters said she was working on getting her fitness back over tennis so far.
"I love the challenge, I like to push myself," Clijsters said. "I'm surprised how, at times when I'm going through a rough practice, how easy it is for me to stick with it and to fight through it and to push through it.
"It's a very satisfying feeling to have that kind of challenge again."
Clijsters said the biggest issue she can see is the effect on her children Jada, 11, Jack, 5, and Blake, 2.
"Of course, if you want to go through a marathon you're not going to have the whole media in your face," Clijsters said. "That was, to me, the toughest part about it. I know that I can handle it, but the kids, that's a different story.
Our life is very easy and simple right now. It's not just my life that is going to change.
"But then obviously I talked about it with my husband and with the team and then with Steve Simon from the WTA about being able to just hold off as much as possible to protect the children, obviously."
WTA chairman and CEO Steve Simon said he was excited to see Clijsters back on court.
"Kim Clijsters ranks among the greats of the game and her return to the Tour is exciting news for the WTA family and tennis fans around the world," Simon said.
"Driven by her love for the sport, this wonderful champion continues to inspire women and men in all walks of life — and she only adds to the compelling wealth of talent in women's tennis. I wish Kim all the best in this next chapter of her playing career."
