Mid 19th century; earliest use found in John Campbell. Probably partly a typographical error for autobiographical, and partly either from autobiograph- + -al or shortened from autobiographical.
Definition of autobiographal in US English:
autobiographal
adjectiveˌɔːtə(ʊ)bʌɪˈɒɡrəfl
Autobiographical.
Origin
Mid 19th century; earliest use found in John Campbell. Probably partly a typographical error for autobiographical, and partly either from autobiograph- + -al or shortened from autobiographical.