The 29-year-old actress-singer recently ended her tour, and has been spotted out on several occasions with a growing baby bump, reported Us magazine.
Meester and Brody, 35, first met on set of 2011's dramedy "The Oranges". While dating, they went on to work together in the 2014 comedy "Life Partners".
After keeping tight-lipped about their romance for several months, the couple secretly wed in 2014. They made their red carpet debut at the Tony Awards four months later.
Brody previously dated his "O C" costar Rachel Bilson.