Do you underline the title of a memoirs?

Yes, in MLA (Modern Language Association) format, a memoir is a type of book, and books should be either underlined or italicized. In AP (Associated Press) format, a memoir should be put in quotations.

Example:

In MLA format: Elie Wiesel's Night is a gripping read. OR Elie Wiesel's Night is a gripping read.

In AP format: Elie Wiesel's "Night" is a gripping read.