ex officio

[Latin ex officiō : ex, from + officiō, ablative of officium, office.]

By right or virtue of the office held; officially. An ex officio member is a member of a board, committee, or other body by virtue of his title to a certain office, and does not require further appointment.

[Latin, From office.] By virtue of the characteristics inherent in the holding of a particular office without the need of specific authorization or appointment.

The phrase ex officio refers to powers that, while not expressly conferred upon an official, are necessarily implied in the office. A judge has ex officio powers of a conservator of the peace.

out of (as a result of) one’s duty or office

The adjective has one meaning:

Meaning #1: by virtue of an office or position

The adverb ex officio has one meaning:

Meaning #1: by virtue of position
  Synonym: by right of office