Nightengale added that the MLB owners unanimously approved the extension.
The 60-year-old Manfred was named commissioner in 2015 following the retirement of Bud Selig.
During his tenure as commissioner, Manfred has primarily focused on trying to increase the pace of play and shorten the length of games.
That began in 2015 when he instituted a rule preventing hitters from exiting the batter's box.
This year, Manfred instituted a rule that limited teams to just six mound visits per game, and while there is no pitch clock at the MLB level yet, they were utilized in Double-A and Triple-A during the 2018 season.
According to Baseball Reference, pace of play rules dropped the time of an average MLB game from 3:07 in 2014 to 3:00 in 2015, but it climbed back up to 3:08 in 2017 before falling to 3:04 last season.
Per Maury Brown of Forbes, 69,625,244 people attended MLB games during the 2018 MLB regular season, which represented a 4 percent drop in per-game attendance from the previous year.
It also marked the first time since 2003 that fewer than 70,000,000 people attended MLB games over the course of a season.
Looking ahead to 2019, Manfred is looking to further MLB's global reach by having the New York Yankees and Boston Red Sox play a two-game series in London in June.