I have one dark tooth in the front. Will regular at-home bleaching make it lighter?

First of all, the cause of the dark tooth must be determined. It could be due to an earlier trauma to the tooth or previous root canal treatment. In such a case external teeth whitening treatments may not help. Your dentist may try internal bleaching which may take several sessions. If not, consider dental bonding, porcelain veneers, or capping the tooth to mask the darkness.