Learn Spanish (Latin America): Todo depende de ti.

In Spanish, the verb depender always pairs with the preposition de, never en. English uses "on", but verb-preposition combinations rarely translate word-for-word between the two languages.

Why doesn't ti have an accent mark? I usually see an accent on mí.

Accent marks on one-syllable words are only used to distinguish between two words that are spelled the same, like mí (me) and mi (my). Because there is no other word spelled ti in Spanish, it never takes an accent mark.

Is todo always followed by a singular verb like depende?

Yes! When todo stands alone as a subject meaning "everything", it acts as a third-person singular pronoun. That is why it takes the singular verb depende.

How could I combine this sentence with a justification marker like Es que...?

You can simply place the marker at the beginning of the sentence to explain or justify a situation. For example, if someone asks why you are waiting for them to act, you could reply: Es que todo depende de ti. (It's just that everything depends on you.)