The One Chicago universe is no stranger to cast shake-ups. Over the years, NBC’s long-running franchise has seen beloved characters come and go, from Jesse Lee Soffer’s shocking exit on Chicago P.D. to Scott Eastwood’s brief stint that ended almost as quickly as it began. But one of the earliest departures that left fans reeling was Charlie Barnett’s Peter Mills on Chicago Fire.

Mills, a second-generation firefighter, was a core member of Firehouse 51 for the first three seasons. His sudden decision to leave Chicago and help run his family’s North Carolina restaurant blindsided fans in 2015. So why was he written out? And how does Barnett feel about it now?

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The Real Reason Peter Mills Was Written Out

According to Chicago Fire executive producer Matt Olmstead, the decision wasn’t personal — it was about keeping the ensemble balanced and the storytelling fresh.

“The hardest part of this job is when you feel it’s the right time to make cast changes,” Olmstead told TV Guide back in 2015. “It was solely based on bringing in new people for new stories. Otherwise, it turns into a clown car.”

Olmstead explained that while the creative team had “affection and admiration” for Barnett, they felt the need to shake things up:

“We wanted to bring in a new character and started discussing the idea … and here we are. It was an extremely tough decision to make, but we feel good about it.”

For viewers, it meant saying goodbye to a fan-favorite firefighter who had grown into a reliable, emotional anchor on the show.

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Though Barnett didn’t choose to leave, his career hardly slowed down. In fact, his post-Chicago Fire résumé has been both diverse and impressive:

• Television highlights: Roles in Secrets and Lies, Valor, Arrow, and Netflix’s Tales of the City and You.

• Breakout streaming success: As Alan Zaveri, opposite Natasha Lyonne, in the critically acclaimed Russian Doll.

• Star Wars universe: Portraying Jedi Knight Yord Fandar in Disney+’s The Acolyte.

• Film work: Between 2022–2024, appeared in comedy (Dance Dads) and drama (Last Weekend, Dreams in Nightmares).

This steady stream of roles has allowed Barnett to showcase his range far beyond the firefighting drama that first introduced him to network audiences.

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From Heartbreak to Gratitude

In a 2022 interview with Digital Spy, Barnett reflected on the sting of being written out — and how it ultimately helped him grow.

“I really was sad to be let go. It broke me for quite a long time,” he admitted. “Yeah. It was a blessing in disguise, and they all told me that. You never really see that in life, in general. You never see the bad moments becoming the good … So, I’m thankful.”

Today, Barnett is proof that what feels like a setback can open doors to bigger opportunities. And while fans may still miss Peter Mills at Firehouse 51, the actor has carved out a thriving career across multiple genres — and seems happier for it.