The announcement came as former Heisman Trophy winner Troy Smith, who had been expected to compete for the starting job, finally returned from a severe tonsil infection that had sidelined him since training camp.
Whether Smith would again compete for the starting job once he returned had been an open question. But Harbaugh said Smith will be the third quarterback behind backup Todd Bouman this week against the Indianapolis Colts, and will eventually compete with Bouman for the No. 2 spot on the depth chart.
"Troy is working full-speed ahead as a healthy quarterback this week really for the first time, which is exciting and great news for us," Harbaugh said.
"[Third-string] will be his role this year, possibly in a role where he can contribute playing quarterback for us down the road," Harbaugh added. "That all remains to be seen by game play and whatnot, and that's where we're at."
he has been treating the job as if it were his from the start, so the vote of confidence doesn't change his outlook.
"That's the way I've been approaching it," Flacco said. "It's just a good opportunity for us to go out there and me to go out there as the quarterback and do as much as I can do to help this team win."
Flacco has taken his lumps of late, throwing two interceptions in a loss to the Tennessee Titans and losing a critical fumble in an overtime loss to the Pittsburgh Steelers. But he still has the support of his top receiver, Derrick Mason.
"Joe, keep playing man," Mason said, according to the Carroll County (Md.) Times. "You can't mess with a quarterback. That's one thing I've found in this league that you can't do. Let a quarterback be a quarterback.
"Sometimes, you're going to hit them. Sometimes, you're going to miss them. Joe has a good track record because he's hit more than he's missed."