"It's happening! I'm going to be a dad!" Lowe, 32, captioned an Instagram photo of the couple smiling and sitting on a couch as he rested one hand on his wife's stomach.
"Hey baby," Giudici, 29, added on her own social media account.
The couple made the big announcement on Tuesday, and love and support has been flowing in ever since.
"Thank you to everyone for the kind words today!" Lowe tweeted December 8. "@clmgiudici and I are so excited!"
Just yesterday, Lowe shared a photo featuring himself and Giudici taking their two dogs on a walk through a park.
"A perfect day with my girls (and possibly a boy)," he wrote, referencing his unborn baby's unknown sex.
Giudici told Extra back in March she wanted to start trying for a baby as soon as possible, at least by the summer.
"Because I want a lot," she admitted. "I want five kids."
Lowe and Giudici got engaged during The Bachelor's seventeenth-season finale which aired in March 2013. They later wed in a live television special for ABC in January 2014.
Since then, Lowe has competed on Dancing with the Stars and the pair participated in an episode of Celebrity Wife Swap, which Lowe came to regret because the show painted him in an unflattering light. The couple is currently starring on Marriage Boot Camp: Reality Stars, which premiered December 4 on WE tv.
However, Lowe and Giudici made it known their marriage was already strong heading into boot camp. They were just open to the idea of strengthening their bond, as The Bachelorette couple Trista Rehn and Ryan Sutter had done years before them.