From the show's inception, Marsh has been one of the main songwriters for the series, along with Dan Povenmire as well as Martin Olson.
In 1996, Marsh won an Environmental Media Association (EMA) Award for Children's Animated Television Program: Rocko's Modern Life, for episode "Zanzibar".
After Phineas and Ferb ended production, Dan and Swampy went on to create Milo Murphy's Law premiering on Disney XD in 2016.
NOTE: Aside from 3 episodes in season 1, Dan Povenmire was his partner for almost entirely of the show. He was paired up with fellow cartoonist Stephen Hillenburg in a few early episodes.
Season 1 (under directed and additional writing):
- Bedfellows (with Stephen Hillenburg)
- Keeping Up With the Bigheads (with Stephen Hillenburg and Mark O'Hare)
- The Good, The Bad, and The Wallaby (with Dan Povenmire)
- Popcorn Pandemonium (with Dan Povenmire)
- A Sucker for the Suck-O-Matic (with Stephen Hillenburg)
Season 2 (Also storyboard):
- Tickled Pinky
- The Lounge Singer
- Road Rash
- Commuted Sentence
- Gutter Balls
- Frog's Best Friend
- Eyes Capades
- Manic Mechanic
- The Fatlands
- Dear John
- Wacky Delly (with Stephen Hillenburg and Mark O'Hare)
- An Elk for Heffer