A phrase meaning 'up until now' or 'even before now', used to indicate that something has already occurred prior to the present moment.
今までにも同じミスが何度かあった。
There have been the same mistakes several times even up until now.
今までにも説明した通り、手順を守ってください。
As explained up until now, please follow the procedure.
今までにも彼女の歌声を聞いたことがある。
I've heard her sing before (prior to now).