Brannan was first known for the voice of Chuck E. Cheese in chains across the U.S. and the English and Spanish voice in national commercials seen on PBS, Nickelodeon, from 1993 to 2012.
He is also known for his work with on the children's TV series Barney & Friends from 1997 to 2002, having provided Barney's character and singing voice for a handful of home video releases, his singing voice for the PBS series and other home video releases, as well as his voice for numerous public relations spots on radio and television and various forms of merchandise, such as plush toys, games, compact discs, and more. He was also Barney's speaking voice in "My Party with Barney", the Barney video that was personalized while Bob West, Barney's original actor, did the singing.
Brannan also works as a freelance writer, speaker, director and fine arts consultant.
NOTE: In most roles, Brannan only supplies Barney's singing voice, while dialogue is voiced by Tim Dever.
- My Party with Barney (1998) (Speaking only, some dialogue)
- Barney's Super Singing Circus (2000) (Singing only)
- Come On Over To Barney's House (2000) (Singing only)
- Barney's Dino Dancin' Tunes (2000) (Singing only)
- Be My Valentine Love, Barney (2000) (Singing only)
- Let's Go to the Zoo (2001) (Singing only)
- You Can Be Anything (2002) (Singing only)
- Barney's Beach Party (2002) (Some speaking dialogue and Singing role)
- Round and Round We Go (2002) (Singing only)
- Barney Rocks! (2000) (Entire role)
- Barney's Theatre (2000-2002) (Entire role)
- Duncan Brannan's voice for Barney sounds similar to Bob West's, but higher-pitched.
- He voiced Barney when he appeared on KNTV.
- Duncan Brannan provided the voice of Barney in part of Season 4 and It's Time For Counting while Bob West and David Joyner left to film Barney's Great Adventure. However, Bob West dubbed over Duncan Brannan's lines when he returned.
- Brannan provided the voice of Barney at the La Brea Tar Pits April 8, 1998 which was in commemoration of the debut of Barney's Great Adventure. He also voiced Barney in the 1999 and 2000 Macy's Thanksgiving Parade.