The Ravens did not disclose terms of the deal, but multiple outlets reported it was for one additional year.
Harbaugh, who was under contract through the 2018 season, is entering his 10th campaign in Baltimore -- making him the sixth-longest tenured head coach in the NFL.
The 54-year-old led the Ravens to the playoffs in his first five seasons, highlighted by a Super Bowl XLVII victory over the San Francisco 49ers following the 2012 campaign.
Harbaugh owns an 85-59 record in the regular season and a 10-5 mark in the playoffs, but has seen his team miss the postseason in three of the past four years.
He is the third head coach in franchise history, alongside Brian Billick and the late Ted Marchibroda.