Marder has performed at most major theaters in the United States as opening act for Jerry Seinfeld.
"Ted L. Nancy" 
Under the pseudonym "Ted L. Nancy" — now a trademark of Marder's — Marder wrote a series of books of prank letters, together with their responses. Books in the series include: Letters from a Nut, More Letters from a Nut, Extra Nutty! Even More Letters from a Nut, Hello Junk Mail!, Ted L. Nancy’s Afternoon Stories, and All New Letters from a Nut. The first three books in the series were co-written with comedian Bruce Baum.
In 2002 ABC developed a pilot for a television series based on Letters From A Nut. It was written and produced by Barry Marder and Jerry Seinfeld. In 2003 FX Television made a pilot for "The Ted L. Nancy Show". That show was written and produced by Marder and Seinfeld. Again in 2007, Lionsgate Television optioned the books from Marder to make into a television show, as reported by Daily Variety. The following year, Lionsgate sold the show as a pilot presentation to Fox TV. That show called Sincerely, Ted L. Nancy is created and written by Seinfeld, Marder and Chuck Martin[disambiguation needed]. Reportedly, Ted L. Nancy is the voice for the underdog consumer who is usually the last to get help from customer service. The show stars Kevin Sussman as the comic hero Ted.
In 2012 it was announced that Scholastic had bought an educational, historical Ted L. Nancy book entitled Ted L. Nancy’s Family Tree. Also in 2012, a promo video for Seinfeld’s widely successful new Internet series "Comedians In Cars Getting Coffee" identifies Marder as Ted L. Nancy and will debut on September 6, 2012.
Roger Friedman of Fox News suggested in 2002 that Barry Marder — a longtime Jerry Seinfeld collaborator and friend — was the real source. His assumption proved true on September 23, 2010, when Seinfeld introduced Marder as the writer "Ted L. Nancy" on Larry King Live on CNN. Seinfeld also appeared with Marder on “The Today Show With Matt Lauer” as the author of the books.
See also 
- "Bee Movie". Retrieved September 6, 2012.
- "Comedians in Cars Getting Coffee". Retrieved September 6, 2012.
- An interesting account of the history of the Ted L. Nancy trademark is found in the complaint in Marder v. John Doe, available here: Marder v. John Doe
- "Shooting Stars: ABC pilot attempts to answer nutty questions". Retrieved 5 September 2012.
- "Nancy, Lionsgate plot 'Nut' job for TV". Retrieved 5 September 2012.
- "Sincerely, Ted L. Nancy". Retrieved 5 September 2012.
- "What Publishing Editors Recently Bought". Retrieved 5 September 2012.
- "Jerry Seinfeld On 'Today Show': Reveals Identity Of Author Behind 'Letters from a Nut". Retrieved 5 September 2012.