ESPN's Field Yates first reported the move, which ensures Elliott will remain with the Cowboys through the 2020 season.
Per Spotrac, the fifth-year option in Elliott's rookie contract is worth $9.099 million, which will be his base salary in 2020 unless a long-term deal is worked out before then.
It was essentially a foregone conclusion that Dallas would exercise Elliott's option, as Cowboys vice president Stephen Jones said last week that the team would "obviously" make the move, per Jon Machota of the Dallas Morning News.
During his three-year NFL career, Elliott has arguably been the biggest key to Dallas' success. In each of the two seasons in which he's has appeared in more than 10 games, the Cowboys have won the NFC East and reached the playoffs.
Elliott also led the NFL in carries and rushing yardage in each of those two campaigns. Last season, Elliott rushed for 1,434 yards and six touchdowns on 304 totes, while also raising his game as a pass-catcher with 77 receptions for 567 yards and three scores.
The two-time Pro Bowler is such a significant part of Dallas' running game that no other running back on the roster had more than 127 rushing yards last season.
Head coach Jason Garrett is not shy about feeding Elliott the ball, and that has helped the Cowboys garner success in a league that is primarily dominated by the passing game.
With Elliott locked in for at least one more season beyond 2019, the Cowboys can shift their focus toward signing him for even longer.
Among running backs, Todd Gurley of the Los Angeles Rams has the NFL's richest contract at $57.5 million over four years, according to Spotrac. He is followed by New York Jets running back Le'Veon Bell, who is set to make $52.5 million over four years.
Given Elliott's workload and the fact that he is just 23, he is in line to surpass both Gurley and Bell en route to becoming the league's highest-paid back.