Ellen Jovin has posted a Twitter survey on her Grammar Table account: Joan is one of the students who _______ (has, have) volunteered to remove the peanut butter and toilet paper from the tree outside the library.
Both are fine. (8.1%)
When you have a pronoun like who, you must identify an antecedent to determine whether it is singular or plural. The noun nearest who in the survey is students. So choose have for the verb.
Students is right there, grimacing, plucking who’s sleeve, but some of you think that who’s eyes are fixed on its distant heart’s desire, one. And a few of you apparently have trouble making up your minds.
Turn the sentence around: Of the students who have volunteered to remove the peanut butter and toilet paper from the tree outside the library, Joan is one. It’s not how a native speaker would construct the sentence, but it shows the grammar. Who among you would write has there?
Much as I choose the plural verb in my own writing, and generally change the singular to the plural when I am editing, and much as Bryan Garner agrees with me on the practice, I can’t make you follow my wholesome example.
English being what it is, a shaggy language, you can find in Merriam-Webster’s Dictionary of English Usage ample evidence that many writers have chosen singular verbs in the one of those who constructions, and continue to do so today. Insisting on one of those who [plural verb], MWDEU suggests, is like Fowler’s that/which distinction, a pious hope.
Just keep in mind that if you choose the singular, you are planting both feet on the slippery slope of notional agreement.
I am one who does not shy from controversy. I am also one of those writers about language who are willing to explain their views in detail.