In both cases it will be who, since 'who' here is the subject of the relative clause(subjective pronoun).

One way to help keep "who" and "whom" straight is to think about "he" and "him". If you would use "him", you should use "whom" - both are objects rather than subjects. Whom can be the subject of a verb or a preposition.

e.g. Whom did you see? I saw him. (Not "I saw he".)

Whom did you speak with? I spoke with him. (Not "I spoke with he".)

I guess this sentence is correct--

The girl,whom i saw in Japan,invited me to her wedding.

GrammarSucks wrote:I guess this sentence is correct--

The girl,whom i saw in Japan,invited me to her wedding.

Correct.

Almost all such sentences have a subject (doer of the action) and an object (receiver of the action). Doer of the action is the subject pronoun (He, who....) and the receiver of the action is the object pronoun (him, whom....)

Notice in this sentence: I saw...

In this, I am clearly the doer of the action seeing. Who did I see? The girl. So, pronoun used for the girl would have to be the object pronoun. Hence, whom, the object pronoun (in this case, referring to the girl) should be used.