Ehasz began his writing career in the year 2000, working as a staff writer on Ed and on Mission Hill. In 2001, he took a position as story editor on Matt Groening's animated Fox series Futurama, on which he worked until its cancellation in 2003. From 2005 until 2008, he served as a co-executive producer and head writer for the acclaimed Nickelodeon children's series Avatar: The Last Airbender. When Futurama was revived by Comedy Central in 2009, he returned to the writing staff. In the same year, he also wrote an episode of the American version of Sit Down, Shut Up.
In 2007, he was nominated for the Outstanding Animated Program (For Programming Less Than One Hour) Emmy award for his work on the second season of Avatar: The Last Airbender.