He was asked to act as an advisor on the project.

act 在这里的意思是"担任、充当"，指扮演某种角色或发挥某种功能。 as 是介词，表示"作为、以...身份"，用于说明某人或某物的角色或功能。 act as 是一个固定搭配，意思是"担任...角色"或"充当...功能"。