Usage patterns
〈委員長〉になるto become committee chairperson
He became class chairperson this year.
〈委員長〉を務めるto serve as committee chairperson
Mr. Tanaka is serving as the executive committee chairperson.
〈委員長〉に選ばれるto be elected/chosen as committee chairperson
She was elected committee chairperson in the student council vote.