“作中间人”常见的英文表达有 "act as a mediator"、"play the role of a middleman" 或 "serve as an intermediary"。具体使用可根据语境调整：
1、 Act as a mediator（侧重调解冲突）
例句： He agreed to act as a mediator in the dispute. （他同意在争端中担任调解人。）
2、 Play the role of a middleman（侧重商业或交易中的中介）
例句： The company plays the role of a middleman between suppliers and buyers. （这家公司在供应商和买家之间充当中间人。）
3、 Serve as an intermediary（通用表达，适用于多种场景）
例句： She served as an intermediary to help both sides reach an agreement. （她作为中间人协助双方达成协议。）
根据语境选择最贴切的短语即可。