The actor also opened up about who his 6-year-old son's favorite Marvel heroes are, and revealed he's not at the top spot.
The handsome star and his bride-to-be made their official red carpet debut as an engaged couple at the premiere of Avengers: Endgame on Monday, and the pair couldn't have looked more adorable as they waved to fans and smiled for the cameras outside the Los Angeles Convention Center.
Pratt shined in a crisp, classic black suit with a silver tie, while Schwarzenegger beautifully complimented his look in a black-and-silver leopard-patterned dress.
ET's Kevin Frazier spoke with Pratt on the star-studded carpet, and the 39-year-old actor opened up about how deep he's getting into the couple's wedding planning.
"I'm up to about my neck, you know? That's pretty deep. That's up to about 5-foot-something," the actor joked. "I'm in it baby, I'm in it. It's good. It's a good time!"
"We're all very blessed," he added. "[It's a] good time to be here for the Avengers premiere and also good things happening for me in life. I just count my blessings every day."
The actor -- who plays Star-Lord, the leader of the Guardians of the Galaxy, in the Marvel Cinematic Universe -- also opened up about the night's big premiere, and admitted that he's not his son's favorite hero from the franchise.
"I'm like Jack's fourth favorite Avenger," Pratt said of his 6-year-old son, whom he shares with ex-wife Anna Faris. "Well, actually, now that there's even more Avengers, I think I'm like ninth favorite."
So who are his son's top tier heroes? "He loves Spider-Man. He's a big Spider-Man fan. He loves Captain America, he loves Black Panther. He loves them all."
ET spoke with Schwarzenegger back in March, at the premiere of the IMAX film Superpower Dogs, where she also reflected on wedding planning, and how much work they've been putting into getting ready for the big day. Check out the video below to hear more.
Avengers: Endgame hits theaters April 26.