IPA: /mɪˈmɔːrɪəlɪst/
KK: /mɪˈmɔːrɪəlɪst/
A person who writes about their own life experiences or memories, often in a book or document.
The memorialist shared her life story in a beautifully written memoir.
Memorialist is formed from "memorial" (from Latin "memorialis", meaning pertaining to memory) and "-ist" (meaning one who practices or is concerned with). The word refers to a person who is concerned with or practices the act of remembering or commemorating.
Think of someone who is 'pertaining to memory' ('memorial') and is an 'expert' or 'practitioner' ('-ist') in remembering or commemorating events.