He will replace Cam Newton, who was 0-5 as the starter after replacing Darnold, who went on injured reserve with a shoulder injury following a Week 9 loss to New England.
"Sam has been working hard to get back," Rhule said. "I thought he did some good things last week. ... We're going to give him this opportunity to show what he can do."
Darnold split time with Newton in Sunday's 32-6 loss to Tampa Bay. He completed 15 of 32 pass attempts for 190 yards.
With the Panthers (5-10) out of playoff contention and Darnold the only quarterback under contract for 2022, Rhule wants to see if the player acquired in a trade with the New York Jets during the offseason can return to the form he was during a 3-0 start.
"I want to see him play the way he did in the first ballgame; he threw the ball on time, was aggressive with his throws," Rhule said. "I'd like to see him play with aggression, be aggressive and play within the system."
Darnold had three passing touchdowns and two rushing with only one interception in leading Carolina to wins against the Jets, New Orleans and Houston. He had his best game against the Saints in Week 2, completing 26 of 38 passes for 305 yards and two touchdowns in the 26-7 victory.
Darnold lost five of his next six starts, throwing 10 interceptions to only four touchdown passes during that span before being placed on injured reserve following a three-interception performance against New England.
The Panthers replaced Darnold with Newton, who had been without a job after being released by the Patriots at the end of training camp. Newton had a storybook return to the team that made him the top pick of the 2011 draft, scoring touchdowns the first two times he touched the ball as a backup to P.J. Walker at Arizona.
Newton, 32, started the next five games, losses to Washington, Miami, Atlanta, Buffalo and Tampa Bay. He had five interceptions and a lost fumble to only one touchdown the past four games, although he did run for three touchdowns.
But because of his age and deteriorating level of play since suffering a shoulder injury in 2018 with Carolina, there are no guarantees he'll be re-signed.
Rhule wouldn't commit to Newton playing at New Orleans.
"Cam's the ultimate professional," he said. "Cam, I can't say enough about him. He had as much energy on the practice field today as anybody."
Darnold said he and Newton have talked since Rhule named him the starter and are "cool with each other.''
"We understand kind of the business that we're in,'' he said. "It kind of is what it is. We're both very professional.
"For me, it's just another opportunity to play good football. That's all I'm focused on, doing my job at the highest level. Nothing more.''
Darnold said his confidence never was shaken during a 1-5 stretch before going on injured reserve.
"During that time I was hurt, I looked at all the games I played,'' he said. "I looked at the good, the ugly. I learned a lot from watching that tape.''
Darnold's also not looking past this game even in terms of how his performance the last two games might impact Carolina's quarterback situation for 2022.
"If I look past this game at all I would be doing this team and myself a disservice by looking too far into the future,'' he said.
The Panthers are committed to Darnold after picking up his fifth-year option following the trade that sent New York a sixth-round pick in 2021, a second- and fourth-round pick in 2022.
Also, Walker, the third-string QB, was placed on the NFL's reserve/COVID-19 list on Wednesday, leaving Carolina with only two quarterbacks for Sunday.
The team currently has 11 players on the COVID list after adding edge rusher Haason Reddick and Walker to the list Wednesday. They were as high as 14 players on Tuesday, but center Pat Elfein and guard Dennis Daley came off the list Wednesday and quarterback Matt Barkley was released.