The UEFA Executive Committee made the decision at its meeting in Dublin, following successful technological testing and the training of referees over the last few months.
As well as being implemented for the UEFA Champions League round of 16 onwards, VAR will also be used for this season's UEFA Europa League final in Baku, the UEFA Nations League Finals in Portugal and the UEFA European Under-21 Championship in Italy.
As already decided during the September meeting of the UEFA Executive Committee, VAR will then be used from the play-off stage of the 2019/20 UEFA Champions League and at the 2019 UEFA Super Cup.
UEFA still plans to extend the use of VAR to the final tournament of UEFA EURO 2020, the 2020/21 UEFA Europa League (group stage onwards), and the 2021 UEFA Nations League Finals.
UEFA President Aleksander Čeferin said: "We are ready to use VAR earlier than initially planned and we are convinced that it will be beneficial for our competitions as it will provide valuable help to match officials and will reduce incorrect decisions."
Various other decisions were made by the UEFA Executive Committee concerning UEFA competitions.
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