"I feel like we both realize that we're parents and we're in it for our kid," the Fall Out Boy star said during an appearance on Bravo's Watch What Happens Live. "That's made it really easy."
Pete added, "I feel like, as a mom, she's awesome. She's an awesome mom and we get along really well when it comes to our kid now."
The 33-year-old musician also had some kind words to say about his former father-in-law, Joe Simpson.
"I think he is a really great grandfather. Really good guy."
Pete and Ashlee divorced in 2011 after three years of marriage.