Answer:
It should be from someone who is obviously a believer and that is also credentialed as a minister or trained to be a lay leader (including deacons, elders, etc).
However, if none are available we also have indication from scripture that anyone who actively evangelizes and leads others to Christ might do this, assuming the conditions were such that no one else could do this.
Acts 8:36-38 And as they went on their way, they came unto a certain water: and the eunuch said, See, here is water; what doth hinder me to be baptized? And Philip said, If thou believest with all thine heart, thou mayest. And he answered and said, I believe that Jesus Christ is the Son of God. And he commanded the chariot to stand still: and they went down both into the water, both Philip and the eunuch; and he baptized him.