This genre straddles the fence between fiction (it is story telling) and non-fiction (it does represent a slice of someone's life). Most agents who seek memoir submissions treat the initial submissions just like they would fiction. Query letter first. Then, if interested, they'll request more information. At some point, they'll want to know about marketing, your platform/following, etc,. At that point, your memoir, will be treated like a non-fiction manuscript, which is quite extensive.
A non-fiction book proposal requires a query letter (written a bit differently that a query for fiction), information about you, the potential market, your platform/following, a full book outline, and, in many cases, the complete manuscript. Some agents require memoirs be submitted as non-fiction projects from the initial contact. To help you figure out what you'll need to prepare, I recommend Michael Larsen's book on how to write a non-fiction book proposal. You can find it on Amazon.
Here's an agent specifically requesting submission of memoirs. Check it out HERE.
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