For Disney, he was best known for voicing Piglet in the Winnie the Pooh franchise, and currently holds the record for the longest running voice actor to ever voice a Winnie the Pooh character, having voiced Piglet for 37 years until his death. Fiedler's final role as Piglet was in Pooh's Heffalump Movie, released in February 2005, four months before his death.
He also voiced the Porcupine in The Fox and the Hound, the Deacon Owl in The Rescuers, Sexton Mouse in Robin Hood, and Rudy in The Emperor's New Groove. He even played Wally Thorpe in Midnight Madness and Charles Blackburn in the 1974 Walt Disney's Wonderful World of Color television movie The Whiz Kid and the Mystery at Riverton. He appeared in The Golden Girls episode "Love Me Tender", playing a love interest of Dorothy.