The 14-year-old British actress joined frontman Adam Levine and the rest of the band onstage Sunady at Bridgestone Arena.
Brown came out on stage in a denim jacket, pink jeans and sunglasses. She rapped Cardi B's verse during the Maroon 5 song "Girls Like You."
"soooo 2nite was insane!!! i love @maroon5 and my dear friend @adamlevine," the actress captioned a video of the performance on Instagram.
The Stranger Things star later gushed about the experience in a series of videos on Instagram Stories.
"It was such an amazing night with such incredible people and such good friends and you know, truly family. It's such an honor to just be on stage with such talented people," Brown said.
"I was not nervous at all going on stage. In fact, I was so comfortable. It was so insane. It was so fantastic. I had such an amazing time," she added.
"Conclusion: I had an amazing night."
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Brown appeared in Maroon 5's music video for "Girls Like You," which debuted in May.
"Had so much fun with @adamlevine on the @maroon5 #GirlsLikeYou music video!! It was such a blast and I loved every second of it! Who else wouldn't want to dance to a great song for a day of work!?" she wrote at the time.
Brown is known for playing Eleven on "Stranger Things," which was renewed in December for a third season on Netflix.
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