From the very beginning to the very end; throughout the entire duration without omission.
映画を最初から最後まで集中して見た。
I watched the movie from beginning to end with full attention.
彼はプロジェクトを最初から最後まで責任を持って担当した。
He took responsibility for the project from start to finish.
最初から最後まで意見が変わらなかった。
His opinion didn't change from the beginning to the end.