Daphne brought to me an answer for Corey, who writes:
I have been represented by an agent for the past two years, but she has not sent out any of my work for the last 14 months. I have written to her to say that I no longer wish to be represented by her. My question is… when submitting to a new agent, do I need to mention up front that I have had representation?
First of all, Corey, did you hear back from your agent? Usually, mailed notification is enough to terminate an agency agreement, but you may want to confirm that she received it, and didn’t take it as an impetus to try to submit something.
But getting onto your question, I think you should say in your query letter to other agents that you have been previously represented, particularly if your previous agent made any sales on your behalf. Are you querying new agents on material that your previous agent represented, or new work? That’s also something you may want to mention.
Basically, I’m a firm proponent of the “be upfront about things, and they won’t come back to bite you in the ass” school of thought. Good luck!