Write a query letter to send to agents. A query letter should include the book’s title, the genre, the word count and a short synopsis of the story. The synopsis should be a teaser, similar to what you might read on the book jacket.
Pick five of your favorite historical authors and find out whom they have as an agent. You can find this on the author’s web page, by searching for the author’s name and the word "agent" on a search engine, or in the acknowledgements page of a book.
Use an agent database to look for agents that represent historical biographies. Agentquery.com and querytracker.net are two databases that allow you to search according to genre. They also list the agents' websites, which allows you to learn more about individual agents.
Research agents according to individual taste and agenting style. Review each agent’s website and client list to find if you are a good match. You can visit the writer’s forum at Absolute Write to read writers' reviews of agents and the querying process.
Query the agents that are the best match for your work by sending in your query letter and any other material that the agent requests.