Roiland was born on February 21, 1980. He grew up on an almond orchard in Manteca with his parents and a younger sister, Amy, a fashion designer. He is well known for being the voice of Oscar on Disney Channel's animated series Fish Hooks, Blendin Blandin on Gravity Falls, and the Earl of Lemongrab on Cartoon Network's popular animated series Adventure Time. He is also well known for his Channel 101 shorts he made in his early career, including such shows as House of Cosbys, starring a man who lives with 100 Bill Cosby clones, and 2 Girls 1 Cup: The Show, an adaptation of the infamous Internet meme, where a cup unsuccessfully tries to have his two roommates take a shit in him.
- Rick Sanchez (and all alternate versions of Rick)
- Morty Smith (and all alternate versions of Morty)
- Mr. Meeseeks
- "Rixty Minutes": Ants in my Eyes Johnson, Gazorpazorpfield, Baby Legs, Real Fake Doors Salesman, Tophat Jones
- Mr. Poopybutthole
- Taddy Mason
- "Interdimensional Cable 2: Tempting Fate": Randy Dicknose, Eyeholes Man, Jan Michael Vincent, Stealy, Comedian, Michael Thompson, Pichael Thompson, Octopus Man
- "Rick Potion No. 9"
- "Rixty Minutes"
- "Interdimensional Cable 2: Tempting Fate"
- "Look Who's Purging Now"
- Justin owns two dogs, with "Jerry" being the inspiration for Snuffles.
- From 2010 to 2013, he co-hosted The Grandma's Virginity Podcast with Ryan Ridley and Jackie Buscarino.
- Provided additional voice work for the Pocket Mortys game.
- Justin is the writer of the humorous descriptions for every episode.