The Painted Turtle is camp founded by Paul Newman in 1999 that helps kids with life-threatening or chronic medical conditions. Zellweger's attendance at the event marked the first time the 44-year-old actress hits the red carper since November.
Zellweger kept it elegant-chic for the occasion in a fitted, three-quarter-sleeve black dress, black shoes and pearls. The Bridget Jones star wore minimum makeup and her hair in a high bun for the event.
Last November Zellweger sparked plastic surgery rumors after looking "unrecognizable" at the screening of Long Shot: The Kevin Laue Story. While many claimed the actress had a chin implant, others said her facial changes were due to her dramatic weight loss.
Other stars to join Zellweger during Monday's charity event included former Glee star and DWTS veteran Amber Riley -- who performed at the event -- as well as Annette Bening, Josh Groban and Kathy Griffin.
Later that night Riley expressed her excitement over meeting Zellweger on Twitter.
Renée Zellweger is probably my new favorite person in life— Amber Patrice Riley (@MsAmberPRiley) March 11, 2014
Earlier this month it was revealed that Zellweger plans to return to the silver screen after a four year hiatus in the upcoming film, The Whole Truth.