A conjunction meaning "in any event" or "at any rate," indicating that the outcome or decision is the same regardless of circumstances.
説明が遅れても、いずれにせよ結果は同じだ。
Even if the explanation is late, in any event the result is the same.
いずれにせよ準備だけは進めておこう。
In any case, let's at least proceed with the preparations.
彼が賛成しようがしまいが、いずれにせよ計画は実行するつもりだ。
Whether he agrees or not, at any rate I intend to carry out the plan.