The 38-year-old, who married Marc in upstate New York in July 2010, shared the exciting news on twitter.
They are already parents to two children, daughter Charlotte, 4, and Aidan, 2. Now the couple will officially be outnumbered.
"Marc and I have loved watching Charlotte be such a wonderful big sister and we’re excited to watch Aidan become a big brother! We cannot wait to meet our newest addition later this summer," she wrote.
The former first daughter has embraced motherhood so much, she written children's books. She promoted her most recent one, "Start Now! You Can Make a Difference,” on The Tonight Show Starring Jimmy Fallon.
Her famous parents, former President Bill Clinton and former Democratic Presidential Nominee Hillary Clinton, have not commented yet, but it's no secret they love their role as grandparents. Following Aidan's birth, the former first lady told supporters in Ohio, "I have to confess, I talk so much about being a grandmother, now I'm sure I'm going to be talking doubly about being a grandmother."
What do you think of the news about Chelsea and Marc's new addition? Let us know in the comments.