The star, who recently married singer Ashlee Simpson, told E! News that he felt "totally content" when he heard the news.
"I'm genuinely a nervous person in general," Wentz said, explaining that he is now "excited to be a dad".
"The first time I ever went to the doctor's office and heard the (baby's) heartbeat, I felt totally content and at peace with everything," he said.
Supportive Pete Celebrates His B-Day Sans Cocktails
Pete Wentz turned 29 yesterday and marked the occasion with a big bash at Foxtail with new wife Ashlee by his side. And although the dad-to-be has lots of reasons to celebrate, a source says he never raised a glass the entire evening.
Looks like Pete's not drinking because Ash can't either...How sweet!
Even without booze, the birthday boy seemed to have a great time. Although Brent Bolthouse had the entire upstairs area reserved exclusively for their party, Pete and Ash spent most of their time downstairs, chatting and shaking hands with regular folks.
She was dressed in a black mini—that didn't show any signs of a belly—and gladiator-style stiletto heels. Pete matched perfectly, wearing black slacks and a button-up.
Around midnight, the waitstaff brought out a a cake for Pete and everyone (including his dad) sang "Happy Birthday."
(It took the Fall Out Boy bassist several tries to blow out his candles, but he finally managed, all while getting frosting smeared down the front of his suit.)
Soon after, the newlyweds called it a night, exiting Foxtail through the front door where they greeted by 30 or so of Pete's closest paparazzi pals.
Pete Wentz: Ready for Daddy Duty
Now that newlyweds Pete Wentz and Ashlee Simpson-Wentz have finally confirmed they're expecting, papa-to-be Pete is ready to open up about the happy news.
"I'm excited to be a dad," he told me at the Op clothing launch party Tuesday night, while admitting he was initially scared. "I'm a genuinely nervous person in general. The first time I ever went to the doctor's office and heard the heartbeat, I felt totally content and at peace with everything. It feels good."
Pete, who came without Ashlee, has a lot to celebrate these days. Besides his new marriage and baby on the way, the Fall Out Boy rocker has an MTV show in the works and turns 29 this Thursday. But he got an early surprise at the bash...
Pete was presented with a huge cake and serenaded by partygoers with an early "Happy Birthday." Wilmer Valderrama, featured alongside Pete in the Op campaign, helped him blow out his candles.
Also on hand to celebrate the new ads: Kristin Cavallari, Rumer Willis, Corbin Bleu and Kim Kardashian.