On June 30, 2015, DeSmith signed a contract for the 2015–16 season with an ECHL team, the Wheeling Nailers, after the NCAA denied a transfer waiver to play a senior season of college hockey.
He would have been ineligible to play college hockey after 2015-2016, because the NCAA normally only allows student-athletes five academic years to use up their standard four seasons of eligibility.

DeSmith would appear in just thirteen total games with the Nailers' 2015–16 Eastern Conference Championship team, posting a 5–2–2 record, a 2.55 goals against average, and a 0.915 save percentage.

On January 3, 2016, DeSmith was loaned to the Nailers' American Hockey League (AHL) affiliate, the Wilkes-Barre/Scranton Penguins.
He played his first game for the WBS Penguins on December 26, 2015, against the Hershey Bears, stopping all seven shots he faced during his 20 minutes of play.
He earned his first win in his first career AHL start on January 3, 2016, against the Hartford Wolf Pack, stopping 22 of 24 shots.
He got his first shutout on April 1, 2017, making twenty-six saves against the Lehigh Valley Phantoms.

DeSmith started the three final games of the 2015–16 AHL season.
He won all three games with a 0.950 save percentage.
He won his first professional playoff game during the Calder Cup Playoffs on April 20, 2016, against the Providence Bruins.
Three days later, he set a Wilkes-Barre/Scranton record for most saves in a playoff game facing 59 shots.
The double overtime win clinched the Penguins' fourth division crown as the #1 ranked team in the Atlantic Division and the Eastern Conference.
The Penguins would ultimately fall to the Hershey Bears.

On July 4, 2016, DeSmith signed a contract directly with the Wilkes-Barre/Scranton Penguins.
He would play in 29 games for the Penguins during the 2016–17 season.
He finished the regular season at the top of the AHL with a 2.01 goals against average and a 0.926 save percentage.
He started all five playoff games for the Penguins after partner Tristan Jarry was called up to Pittsburgh during the 2016–17 Stanley Cup playoffs.
He and Jarry would end the season as the best goaltending tandem in the AHL.
The duo was awarded the 2017 Harry "Hap" Holmes Award.
DeSmith was voted by coaches, players and media in each of the league's thirty teams to the AHL's 2016–17 All-Rookie Team along with teammate Jake Guentzel.
After the Wilkes-Barre/Scranton season ended, DeSmith returned to Pittsburgh and served as a "Black Ace" during the Pittsburgh Penguins' 2017 Stanley Cup run.

On July 1, 2017, DeSmith signed his first NHL contract (one-year, two-way) with the Pittsburgh Penguins.
He started the 2017–18 AHL season with a 3–0 record with a 0.98 goals against average, a 0.965 save percentage, and one shutout.
He ranked second in the AHL in goal-against average and third in save percentage.
On October 23, 2017, executive vice president and general manager Jim Rutherford announced that the Penguins had recalled DeSmith from Wilkes-Barre/Scranton.
He played in his first NHL game on October 29, 2017 against the Winnipeg Jets at Bell MTS Place after head coach Mike Sullivan pulled starting goaltender Matt Murray in the first period.
In doing so, he became the 62nd former Nailer/Thunderbird to reach the NHL and the first member of the 2015–16 Eastern Conference Championship team to reach the NHL.
10 seconds into DeSmith's NHL debut, he faced his first career shot, a goal by forward Blake Wheeler.
In the end, DeSmith made twelve out of fifteen saves in a little over forty minutes of play.
He made his first NHL save against forward Patrik Laine.
On October 30, 2017, he was reassigned back to the Wilkes-Barre/Scranton Penguins.

DeSmith was recalled on November 28, 2017, to play backup to Tristan Jarry after starting goalie Matt Murray was injured.
In a game against the Toronto Maple Leafs on December 9, he filled in for Jarry in the second period marking his second NHL appearance.
Despite his efforts, the Penguins ended up losing 3–4.
He was reassigned to the Wilkes-Barre/Scranton Penguins a game later as Murray was ac
On June 30, 2015, DeSmith signed a contract for the 2015–16 season with an ECHL team, the Wheeling Nailers, after the NCAA denied a transfer waiver to play a senior season of college hockey. He would have been ineligible to play college hockey after 2015-2016, because the NCAA normally only allows student-athletes five academic years to use up their standard four seasons of eligibility.
DeSmith would appear in just thirteen total games with the Nailers' 2015–16 Eastern Conference Championship team, posting a 5–2–2 record, a 2.55 goals against average, and a 0.915 save percentage.
On January 3, 2016, DeSmith was loaned to the Nailers' American Hockey League (AHL) affiliate, the Wilkes-Barre/Scranton Penguins. He played his first game for the WBS Penguins on December 26, 2015, against the Hershey Bears, stopping all seven shots he faced during his 20 minutes of play. He earned his first win in his first career AHL start on January 3, 2016, against the Hartford Wolf Pack, stopping 22 of 24 shots. He got his first shutout on April 1, 2017, making twenty-six saves against the Lehigh Valley Phantoms.
DeSmith started the three final games of the 2015–16 AHL season. He won all three games with a 0.950 save percentage. He won his first professional playoff game during the Calder Cup Playoffs on April 20, 2016, against the Providence Bruins. Three days later, he set a Wilkes-Barre/Scranton record for most saves in a playoff game facing 59 shots. The double overtime win clinched the Penguins' fourth division crown as the #1 ranked team in the Atlantic Division and the Eastern Conference. The Penguins would ultimately fall to the Hershey Bears.
On July 4, 2016, DeSmith signed a contract directly with the Wilkes-Barre/Scranton Penguins. He would play in 29 games for the Penguins during the 2016–17 season. He finished the regular season at the top of the AHL with a 2.01 goals against average and a 0.926 save percentage. He started all five playoff games for the Penguins after partner Tristan Jarry was called up to Pittsburgh during the 2016–17 Stanley Cup playoffs. He and Jarry would end the season as the best goaltending tandem in the AHL. The duo was awarded the 2017 Harry "Hap" Holmes Award. DeSmith was voted by coaches, players and media in each of the league's thirty teams to the AHL's 2016–17 All-Rookie Team along with teammate Jake Guentzel. After the Wilkes-Barre/Scranton season ended, DeSmith returned to Pittsburgh and served as a "Black Ace" during the Pittsburgh Penguins' 2017 Stanley Cup run.
On July 1, 2017, DeSmith signed his first NHL contract (one-year, two-way) with the Pittsburgh Penguins. He started the 2017–18 AHL season with a 3–0 record with a 0.98 goals against average, a 0.965 save percentage, and one shutout. He ranked second in the AHL in goal-against average and third in save percentage. On October 23, 2017, executive vice president and general manager Jim Rutherford announced that the Penguins had recalled DeSmith from Wilkes-Barre/Scranton. He played in his first NHL game on October 29, 2017 against the Winnipeg Jets at Bell MTS Place after head coach Mike Sullivan pulled starting goaltender Matt Murray in the first period. In doing so, he became the 62nd former Nailer/Thunderbird to reach the NHL and the first member of the 2015–16 Eastern Conference Championship team to reach the NHL. 10 seconds into DeSmith's NHL debut, he faced his first career shot, a goal by forward Blake Wheeler. In the end, DeSmith made twelve out of fifteen saves in a little over forty minutes of play. He made his first NHL save against forward Patrik Laine. On October 30, 2017, he was reassigned back to the Wilkes-Barre/Scranton Penguins.
DeSmith was recalled on November 28, 2017, to play backup to Tristan Jarry after starting goalie Matt Murray was injured. In a game against the Toronto Maple Leafs on December 9, he filled in for Jarry in the second period marking his second NHL appearance. Despite his efforts, the Penguins ended up losing 3–4. He was reassigned to the Wilkes-Barre/Scranton Penguins a game later as Murray was ac
Casey DeSmith