grammar question: me vs. my ?

I believe its me

It would be either

"this lead to me being promoted"

or

"this lead to my promotion"

Me is pronoun; my is pronomial adjective.. @TruMobius got it in one. Our language gets very confusing. Woe is I.

I'd recommend less passive language to avoid this problem completely. For example,
"This action necessitated my promotion." (Or "fostered," or any other active verb).

It is a valid question though.

Actually I think it's my. I remember learning that when a pronoun precedes a gerund (-ing) verb, you need the possessive form of the pronoun. As if the action belongs to that person.

You should use the possessive adjective, "my."

The promotion is the object of the verb "led." If "me" were the object of the verb (e.g., "The trail of evidence led to me.") then you would use me, which is an object pronoun. Since the object of the verb is "being promoted," use the possessive adjective to indicate that it's your promotion.

Usually we don't make this distinction in spoken English, and it might sound stuffy to use the possessive pronoun among friends. But in written English, and especially on resumes or in business documents, the possessive adjective is definitely preferable.

Here's a more thorough explanation of the general rule.

I agree with Ben, though, that it's simpler (and better) to say "my promotion" rather than "my being promoted," and if you can phrase your promotion as something that you brought about actively, rather than passively, then all the better.

I agree with Ben. Toss out those "be" verbs that cause a sentence to stagnate. Action, man, action.

I disagree with Ben. You can use either object or possessive pronouns before gerunds. It depends on the emphasis you want to convey.

The argument that gerunds are nouns, therefore must be used with possessive pronouns, doesn’t work. Gerunds have noun-like properties in that they can be preceded by possessives, ie “my being promoted”, but they also have verb-like properties in that they can be followed by objects, ie “would you mind me/my borrowing your cell phone?”