・He need not have done it. ＝He doesn't need [have] to do it. それをするには及ばなかった(のにした) (cf. He didn't need [have] to do it.

複数辞典一括検索+

・He need not have done it. ＝He doesn't need [have] to do it. それをするには及ばなかった(のにした) (cf. He didn't need [have] to do it.🔗⭐🔉

・He need not have done it. ＝He doesn't need [have] to do it. それをするには及ばなかった(のにした) (cf. He didn't need [have] to do it. する必要がなかった(のでしなかった)).

研究社新英和大辞典ページ 207216 での【のにした】単語。