“作主席”常见的英文表达是“serve as the chairperson” 或 “act as the chairman/chairwoman”（根据性别选择 chairman 或 chairwoman ）。例如：
He will serve as the chairperson at this meeting.（他将在这次会议上作主席。）
She acted as the chairwoman during the negotiation.（她在谈判期间作主席 。）