The reality star posted a photo Wednesday on her official Instagram account of her and NBA player boyfriend Tristan Thompson cradling her pregnant belly.
"My greatest dream realized," the caption read. "We are having a baby!"
Kardashian, who has been open in the past about her fertility issues, wrote, "I had been waiting and wondering but God had a plan all along."
"He knew what He was doing," she wrote. "I simply had to trust in Him and be patient."
Her desire to start a family had been part of the storyline on her former reality show "Khloe & Lamar" with now ex-husband and former NBA player Lamar Odom (the couple were estranged for some time before legally divorcing last December).
Reports surfaced in September that Kardashian was pregnant by boyfriend Thompson, who plays for the Cleveland Cavaliers.
The news came right after reports that her younger sister, Kylie Jenner, was also pregnant with her first child by rapper boyfriend Travis Scott.
A source close to the family told CNN Kylie is due in February.
Kardashian explained the reason for her and Thompson's secrecy in her posting.
"I know we've been keeping this quiet but we wanted to enjoy this between our family and close friends as long as we could privately," she wrote. "To enjoy our first precious moments just us."
Thompson reportedly has a son by former girlfriend Jordan Craig.
It's been a bumper year for the Kardashian-Jenner clan in terms of babies.
Kim Kardashian West and rapper husband Kanye West are also expecting a child, their third, via a surrogate.