"Guarantee it," Harbaugh said on "The Rich Eisen Show."
Jackson will make a guaranteed $23.1 million in 2022, a significant raise from his $1.7 million salary this season. This will be the highest fifth-year option in the league next season, tying that of Buffalo Bills quarterback Josh Allen.
By exercising Jackson's option, the Ravens will squash the speculation that the team will allow Jackson to "graduate" after four seasons. An NFL Network analyst recently suggested the Ravens could trade up to draft a quarterback this week and move on from Jackson before his heightened salary-cap hit limits Baltimore's spending.
Harbaugh made it clear that won't be the case.
"He's definitely going to be our quarterback," Harbaugh said. "That's the plan, absolutely."
Jackson, 24, has won more games (30) than any other NFL quarterback since taking over as Baltimore's starter midway through the 2018 season. and he became the second unanimous league MVP in 2019. He is the first player in NFL history to produce 5,000 yards passing and 2,500 yards rushing in his first three seasons.
Harbaugh pointed out how the Ravens have scored more points than any other team in Jackson's two full seasons as a starting quarterback.
"I feel like it all points to one thing and the thing he talks about all the time: He wants to win a Super Bowl," Harbaugh said. "I think he's a very unique guy. He's a guy that's different in a lot of ways than any quarterback that's ever played. Lamar is somebody that just kind of breaks the mold a little bit. He does it in a way that a lot of people didn't anticipate. They didn't see this coming. He's very determined -- and we're very determined -- to prove those people wrong."
In March, Ravens general manager Eric DeCosta said the team is "confident and committed" to getting a long-term deal done with Jackson.