Usage patterns
〈人〉が大臣に任命されるto be appointed as a minister
He was appointed finance minister last month.
大臣を務めるto serve as a minister
She served as foreign minister for five years.
大臣を辞任するto resign as a minister
He resigned as minister after the scandal.
〈人〉が大臣になるfor someone to become a minister
He says he wants to become a minister someday.