Jason Mendelson is the son of animation executive Lee Mendelson. He provided the voice of Rerun van Pelt in the 1983 season of The Charlie Brown and Snoopy Show. He was the voice of Marcie in Happy New Year, Charlie Brown!, the voice of Milo in It's an Adventure, Charlie Brown and the voice of Peppermint Patty in This is America, Charlie Brown.
Later on, Jason Mendelson worked as a story developer on He's a Bully, Charlie Brown, I Want a Dog for Christmas, Charlie Brown, Lucy Must Be Traded, Charlie Brown, Charlie Brown's Christmas Tales and A Charlie Brown Valentine. He worked as a producer on It's Your 50th Christmas, Charlie Brown, in which he also appears in archive footage, and as a producer and editor on The Making of A Charlie Brown Christmas.