From Longman Dictionary of Contemporary Englishex-officioex-of‧fi‧ci‧o /ˌeks əˈfɪʃiəʊ $ -ʃioʊ/ adjective formal SSOan ex-officio member of an organization is only a member because of their rank or position —ex officio adverb
Examples from the Corpus
ex-officio• The presidium would no longer have ex-officio members.From Longman Business Dictionaryex officioex of‧fi‧ci‧o /ˌeks əˈfɪʃiəʊ-oʊ/ adjective an ex officio member of a group or organization is a member because of their senior rank or position, not because they have been chosen by othersThe National Assembly is composed of 228 members: 168 directly elected, 25 ex officio, and 35 indirectly elected. —ex officio adverbThe delegates don’t have to be elected, they can go to these conventions ex officio by virtue of being union officers. 