- Space Command Redemption
2024 Greg Mazzey
- Babylon 5: The Road Home
2023 Lennier (voice)
- Lost in Space
2018 Real Dr. Smith
- The Loud House
2016 Timothy Mccole
- Bravest Warriors
2012 Ralph Waldo Pickle Chips
- Ben 10: Ultimate Alien
2010 Agent Bryson (voice)
- The Face is Familiar
2009 Narrator
- Holly Hobbie and Friends: Surprise Party
2007 Bud Morris (voice)
- A.I. Assault
2006 Major Keith
- Holly Hobbie and Friends: Christmas Wishes
2006 Bud Morris / Judge #1 (voice)
- Holly Hobbie & Friends
2006 Bud Morris (voice)
- Comic Book: The Movie
2004 Bill Mumy
- The Twilight Zone
2002 Story
- What's New, Scooby-Doo?
2002 Harry Noze (voice)
- Crossing Jordan
2001 Paper Shredder Operator
- TVography
2001
- Behind the Dementia
2000 himself
- Buzz Lightyear of Star Command
2000 Eon (voice)
- Attack of the 50 Foot Monster Mania
1999 Narrator
- Lost in Space Forever
1998 Writer
- Underground Adventure
1996 Sam (voice)
- The Monkey Prince
1996 Sam (voice)
- Space Cases
1996 Creator
- Three Wishes
1995 Neighbor
- A Bewitched Christmas
1994 Michael (as Billy Mumy)
- Babylon 5
1994 Lennier
- The Steven Banks Show
1994 Billy Mumy
- Diagnosis: Murder
1993 Parker Craddick
- Star Trek: Deep Space Nine
1993 Kellin
- Animaniacs
1993 The Farmer (voice)
- Double Trouble
1992 Bob
- Batman: The Animated Series
1992 The Fox (voice)
- Captain America
1990 Young General Fleming
- The Flash
1990 Roger Braintree
- Superboy
1988
- Zabagabee
1987 Writer
- Matlock
1986 Dr. Irwin Bruckner
- Hard to Hold
1984 The James Roberts Band - Keyboard
- Twilight Zone: The Movie
1983 Tim
- Fish Heads
1980 Musician
- Sunshine Christmas
1977 Weaver
- Archie
1976 Larry
- Sunshine
1975 Weaver
- Saturday Night Live
1975 Art Barnes (uncredited)
- The Rockford Files: Backlash of the Hunter
1974 Nick Butler
- The Rockford Files
1974 Trask
- Papillon
1973 Lariot
- Sunshine
1973 Weaver
- Bless the Beasts & Children
1971 Lawrence Teft
- Rascal
1969 Sterling North
- Wild in the Streets
1968 Boy (uncredited)
- Lancer
1968
- Dear Brigitte
1965 Erasmus 'Ras' Leaf
- Lost in Space - No Place to Hide
1965 Will Robinson
- I Dream of Jeannie
1965 Custer
- Lost in Space
1965 Will Robinson
- For the Love of Willadean
1964 Freddy Gray
- The Munsters
1964
- Bewitched
1964 Michael
- A Ticklish Affair
1963 Alex Martin
- A Child Is Waiting
1963 Child
- Palm Springs Weekend
1963 Boom Boom Yates
- The Fugitive
1963 David Taft
- Vacation Playhouse
1963 Chris Williams
- The Greatest Show on Earth
1963 Jeff
- Sammy, the Way-Out Seal
1962 Petey Loomis
- Going My Way
1962
- The Virginian
1962 Willy
- The Alfred Hitchcock Hour
1962 Tony Mitchell
- Tammy Tell Me True
1961 Neil Bateman
- The Wizard of Baghdad
1961 Aladdin
- Ben Casey
1961
- Dr. Kildare
1961 Jeffey
- National Velvet
1960
- The Twilight Zone
1959 Anthony Fremont
- Perry Mason
1957 Miles
- Wagon Train
1957 Toddy
- Have Gun, Will Travel
1957 Little Boy at Carlton Hotel
- Alfred Hitchcock Presents
1955 Jackie Chester
- The Wonderful World of Disney
1954 Petey Loomis
- General Electric Theater
1953 Buzz
- Letter to Loretta
1953 Rennie
- The Jack Benny Program
1950 Little Boy Who Weighs Himself
