に先立ち|にさきだち

Prior to / in advance of. Marks a significant event, and the main clause describes an action done beforehand, typically preparation or a preliminary step such as setting up or giving instructions.

A formal, written-style expression used in announcements, news reports, speeches and official documents about ceremonies, matches, openings and similar events. It is the continuative (中止形) counterpart of に先立って and sounds slightly stiffer. Unlike plain 前に, it implies that the upcoming event is important and the main-clause action is preparation for it.

• 1.
  〜に先立ってN2に先立って is the 「て形」 form: its meaning and how it attaches are the same as に先立ち, and the two are interchangeable when describing preparations, explanations, and the like made before a formal event. It is slightly less formal than に先立ち but still belongs to written style and, likewise, is not used for everyday trivial matters.
• 2.
  に先駆けてN1に先駆けて more strongly emphasizes getting in ahead of others, taking the lead, or breaking new ground, and it often pairs with words like 「他社」 and 「世界」. It normally attaches only to nouns, not directly to a verb's 「辞書形」; when it means 'before something begins' it can often be swapped with に先立ち, but it usually carries a nuance of kicking things off or leading the way.
• 3.
  に際してN2に際して refers to the very moment something begins or arrives, while に先立ち stresses the period before that; に際して has no sense of 'being ahead of others.' The two attach the same way and are both formal, but they mark different points in time, so swapping them changes the meaning.
• 4.
  にあたってN2にあたって means 'on the occasion of' and can refer to the time when the event itself takes place, such as giving a speech at a meeting, whereas に先立ち refers only to beforehand. The two are interchangeable when talking about advance preparation, but にあたって has no usage of 'being ahead of others.'
• 5.
  上でN3When 上で attaches to a verb's 「た形」 or to noun + の, it means doing the second action after completing the first — the opposite time direction from に先立ち's 'before...'; when it attaches to a 「辞書形」 or noun + の, it means 'in the area of.' The two cannot be interchanged.

〜に先立って has the same meaning in て-form and is slightly less stiff; に先駆けて means doing something first, ahead of others or of a trend; に際して and にあたって mark the occasion or time of an event rather than a step strictly before it. 上で after the た-form means 'after first doing X, then Y', while after the dictionary form it means 'in doing X / for the purpose of X' (e.g., 仕事をする上で).