Early 19th century; earliest use found in The British Critic, quarterly theological review, and ecclesiastical record. From auto- + biographist, after autobiography.
Definition of autobiographist in US English:
autobiographist
nounˌɔːtə(ʊ)bʌɪˈɒɡrəfɪst
rare
Autobiographer.
Origin
Early 19th century; earliest use found in The British Critic, quarterly theological review, and ecclesiastical record. From auto- + biographist, after autobiography.