The International FA Board (IFAB) gave their approval to the extra assistants, one next to each goal, to be used in competitions following an experimental period.
IFAB also gave the go-ahead to goal-line technology but, with UEFA president Michel Platini a firm opponent, the systems will not be used in European competition for the foreseeable future.
UEFA said in a statement: "In essence, the additional assistant referees provide two extra pairs of eyes to monitor the game and ensure that the Laws of the Game are upheld.
"They inform the referee of incidents of any kind that he may otherwise have missed, particularly in key areas of the field like the penalty area and its surroundings.
"The referee will remain in sole charge of the match, and the only match official with decision-making powers."
A report by UEFA following Euro 2012 found there were many more accurate offside decisions than in the past - explained by the assistant referees being able to concentrate on offsides and leaving the officials next to the goal to watch for foul play.
UEFA will continue with the use of additional assistant referees from the play-off matches of the coming season's Champions League, and the group stage of the Europa League as well as the UEFA Super Cup.