Translation

運命を左右する / 重大な / 決定的な

Meaning

Fateful describes an event, choice, meeting, or moment that has important consequences for the future, often in a dramatic or history-changing way. It does not mean deadly. Do not confuse it with fatal, which means causing death or complete failure.

Examples

• その運命的な会議が会社の方向を変えました。
  That fateful meeting changed the direction of the company.
• 彼女はその重大な決断を後に何度も思い返しました。
  She often thought back to that fateful decision.