I would not be so sure. A lot of grammarians have written about this, but there seems no consensus.
For the general reader who does not have time to go through all the grammar books, here is an entry from Wikipedia, quoting one grammarian :
In relative clauses, who (like other relative pronouns) takes the number (singular or plural) of its antecedent. Who also takes the person (first, second or third) of its antecedent:
I, who am having a hard time right now, won't be able to help you.
I, a tired old man who is fed up with all your nonsense, refuse to help you.
note 2 is : Bernstein, The Careful Writer, Atheneum (1986), p. 479.
I who am your fellow countryman.
I who love Rome.
And you would all be too highbrow to know Tom Jones's "I who have nothing".
Would you say, "I who has nothing"?
I am almost certain Fowler said the verb should follow I, unless you put 'a man' in between!
Let those who are truly erudite come forward to enlighten us!