Used to indicate that something is increasing or becoming more intense (more and more).
寒くなってきて、いよいよ冬本番だ。
It's getting colder — winter is really here at last.
練習を重ねるうちに、いよいよ動きが速くなってきた。
As they practiced more, their movements became increasingly faster.
締め切りが近づいて、仕事はいよいよ忙しくなった。
As the deadline approached, work got busier and busier.
Indicates that something expected or awaited has finally happened (at last, finally).
いよいよ明日から新しい仕事が始まる。
My new job finally starts tomorrow.
長年の研究の末、いよいよ実験に成功した。
After years of research, they finally succeeded in the experiment.
いよいよ決勝戦。気を引き締めていこう。
The final match is finally here. Let's focus.
Refers to a critical, last-minute, or worst possible moment (at the last moment / the critical point).
いよいよの時に助けが来て、本当にほっとした。
Help arrived at the critical moment, and I was really relieved.
発表直前に資料が消えてしまい、いよいよの場面で困った。
The materials disappeared just before the presentation — I was in trouble at the worst possible moment.
いよいよ出発しようというその時に雨が降り出した。
Just as we were about to leave, it started to rain.