The former first daughter, 34, made the big reveal in New York City at an event hosted by the Clinton Foundation.
“We have our first child arriving later this year,” Clinton said, according to reports.
Hillary Clinton, 66, attended the event and said she is “really excited” to welcome her first granddaughter.
"I just hope that I will be as good a mom to my child and hopefully children as my mom was to me,” Clinton said.
In an interview with Glamour magazine last October, Clinton said she and her husband, Marc Mezvinsky, were ready to start a family.
“We want, God willing, to start a family. So we decided to make 2014 the Year of the Baby,” she said at the time.
Clinton married Mezvinsky in 2010.
“And please, call my mother and tell her that. She asks us about it every single day,” she told Glamour.
In September, former President Clinton was asked on “CBS This Morning” which role — between grandmother and president — Hillary Clinton would prefer taking on.
“If you ask her, I think she’d say grandmother. But I have found it best not to discuss that issue,” he said with a laugh.
“My goal is to live to be a grandfather. The rest of it is out of my hands,” Bill Clinton added.Hillary Clinton, considered the leading Democratic 2016 presidential contender if she runs, tweeted after the announcement that "grandmother-to-be" is her "most exciting title yet."
My most exciting title yet: Grandmother-To-Be! @billclinton and I are thrilled that Chelsea and Marc are expecting their first child!— Hillary Clinton (@HillaryClinton) April 17, 2014