First-year head coach Kyle Shanahan told his quarterbacks about the switch Tuesday, per Matt Barrows of the Sacramento Bee.
Garoppolo gave the 49ers a taste of what he can do when he took over for an injured Beathard on their final drive in Week 12 against the Seattle Seahawks. He went 2-of-2 for 18 yards and connected with Louis Murphy for a touchdown on the final play of the game.
The combination of Beathard and Brian Hoyer did not work for the 49ers and Shanahan. That duo had eight touchdowns and 10 interceptions with a completion percentage of 56.4.
Needing to find a quarterback that can lead them into the future, the 49ers pulled off a shocking deal Oct. 30 to acquire Garoppolo from the New England Patriots for a 2018 second-round draft pick.
A second-round pick himself in 2014, Garoppolo has a limited NFL sample size to evaluate since he played behind Tom Brady. His longest look came at the start of the 2016 season, when Brady was suspended for four games, and he started New England's first two games with excellent results:
There was never any question Garoppolo was going to start for San Francisco. It just became a question of when Shanahan felt comfortable inserting him into the lineup.
Garoppolo can become a free agent this offseason, so the 49ers have to see what their newest asset can do before they negotiate a long-term deal with him.
As ESPN.com's Nick Wagoner noted, the 49ers are set up well with those question marks looming:
"Barring that, the Niners are set to have more than $90 million in cap space in the offseason (after they roll over what's left on this year's cap) -- money they could put toward an extension or, if they wanted to take a longer look at Garoppolo, a franchise tag.
"Simply put, by making the trade instead of trying to pursue Garoppolo as a free agent, the 49ers have assured themselves some level of control over a player who might just be the answer at quarterback while also leaving themselves open to a world of possibilities."
Garoppolo is carrying a heavy burden as the potential long-term answer at quarterback for a team that is 1-10 this season. After playing second fiddle to Brady for three years in New England, he finally has his opportunity to lead an NFL franchise.
The 49ers paid a steep price to acquire Garoppolo, but it will pale in comparison to what they receive if he turns into a top-tier starting quarterback. On Sunday, he'll get his first crack at proving he can be just that.