Browns coach Mike Pettine announced the decision Tuesday afternoon. The team informed Manziel and Brian Hoyer, who has started Cleveland's first 13 games this season, earlier in the day of its decision, sources confirmed. The Browns made the decision internally on Monday, according to a source.
"This decision is really not about Brian Hoyer or Johnny Manziel, it is about the Cleveland Browns. We are always going to make decisions that we feel are in the best interest of the team," Pettine said in a statement. "Brian has done everything that has been asked of him and he has done so as a true professional. ... We are trying to get the offense to perform at a higher level. Johnny has worked very hard to earn this opportunity and it will be very important for every member of the offense to elevate their play for us to obtain our desired result."
Cleveland's choice to start Manziel was reported earlier Tuesday by Fox Sports.
"I'm very appreciative of the opportunity that Coach Pettine and the coaching staff have given me to be the starter on Sunday," Manziel said in the statement. "I've tried to spend my entire season learning what it takes to become a pro and it's been great to watch Brian because he knows what it takes."
Manziel was not expected to make any additional comments Tuesday as he's focused on preparation for his first start, a source said. He is expected to address the media from the locker room Wednesday.
Pettine indicated that he was leaning toward a quarterback change during his news conference Monday, one day after Hoyer struggled in a loss to the Indianapolis Colts.
"Although I am disappointed by coach's decision, I respect him and his choice and will be there to support Johnny," Hoyer said. "As always, I will do whatever I can to help this team win."
Manziel, whose debut start will come in Cleveland's final home game, will have three games to show the Browns (7-6) if he can be the franchise quarterback they've coveted for two decades. Manziel is the Browns' 21st starting quarterback since 1999.
Cleveland has lost three of its last four games but can remain in serious postseason contention with a win Sunday over rival Cincinnati (8-4-1), which leads the AFC North by one-half game.
Even before Manziel was told he'll start, the possibility sparked some controversy, with Bengals coach Marvin Lewis calling the 6-foot rookie "a midget" on Monday night. Lewis later apologized, but the jab stirred up the Ohio rivalry.
Manziel replaced an ineffective Hoyer against the Bills on Nov. 30, and orchestrated an 80-yard touchdown drive, completing three of his first four passes for 54 yards. Pettine was impressed with that drive but acknowledged that the Bills were playing a prevent defense and that the sequence wasn't a true test of what Manziel might have faced against Indianapolis.
Hoyer has orchestrated just one touchdown drive in his last 29 series, according to ESPN Stats & Information. He played well to start the year and led the Browns to a 7-4 record but has struggled mightily the past five games.
In Sunday's 25-24 loss to the Colts, Hoyer completed 14 of 31 passes for 140 yards and two interceptions.
The Browns selected Manziel, 22, with the 22nd overall pick in this year's draft out of Texas A&M, where he won the Heisman Trophy as a freshman in 2012.
Manziel's promotion could signal the end of Hoyer's time with the Browns. A Cleveland-area native who grew up attending Browns games with his father, Hoyer, who battled back from a season-ending knee injury in 2013, is in the final year of his contract. With Manziel as the starter, Hoyer likely will have to sign elsewhere if he wants to remain a starter.
The Browns' switch at quarterback didn't affect the oddsmakers in Las Vegas, as Cleveland stayed as a pick 'em Tuesday.
Asked if there had been any reaction from bettors to the news, Ed Salmons, head football oddsmaker at the Westgate SuperBook said, "None." Added: Nick Bodganovich, director of trading at William Hill: "Not one bit."
The ticket market, meanwhile, did see a jump.
The average list price on the resale market for Sunday's game has gone from $123.78 to $169.49 (36.93 percent increase), according to resale ticket aggregator TiqIQ.
Cleveland ticket broker Mark Klang, who says his company Amazing Tickets is the Browns' largest ticket-holder, said sales picked up Tuesday, despite prices increasing.
"Our prices are about 15 higher so far," Klang said. "If this keeps up the rest of day and evening, I expect prices will jump another 10 percent in the morning."
Manziel couldn't beat out Hoyer during training camp and the rookie's off-the-field behavior, which included weekend trips to Las Vegas, led to outside criticism of his maturity and commitment. The Browns held off on playing him until they felt he was ready, and now Pettine has put the team's season in Manziel's hands.
ESPN.com's Jeremy Fowler, David Purdum and Darren Rovell and The Associated Press contributed to this report.