Briscoe was born in Newark, New Jersey. He grew up in Newark until his later years when he moved to Union, New Jersey. His father, George Briscoe, is a hall of famer and former guard at Stockton State College, his sister, Iasia Hemingway, played at Syracuse University and his cousin, Kyrie Irving, is an NBA player. When he was in seventh grade, he was not selected to an elite AAU team, which fueled his determination. After his eighth-grade year at Kawameeh Middle School in Union, Briscoe repeated the grade at Good Shepherd Academy in Irvington. He was invited to the LeBron James Skills Academy. Briscoe played well, using his body to get to the rim, he was advanced physically for his age. Briscoe was one of only three players from the 2015 class to be invited. After the eighth grade, He attended Saint Benedict's Preparatory School. He teamed with current Fenerbahçe Basketball point guard, Tyler Ennis, to lead the Gray Bees to the brink of an ESPN National High School Invitational championship. They lost on a last-second 3-pointer to Montverde Academy, 67-65. Briscoe had 11 points in the game. Isaiah averaged 15.1 points, 4.6 assists, 3.5 rebounds and 2.3 steals his sophomore season for the 32-2 Gray Bees. Briscoe transferred Roselle Catholic High School for his junior year, where he was coached by Dave Boff. He led the team to state titles in 2014 and 2015. As a senior, Briscoe averaged 21 points, five rebounds and three assists per game. He models his game after Deron Williams and Tyreke Evans. Prior to his senior year, Briscoe led the AAU New Jersey Playaz to the championship at the 2014 Nike Peach Jam in South Carolina. He posted averages of 19.2 points and 5 assists over 23 total games in the Nike Elite Youth Basketball League in 2014. Isaiah finished as Rivals.com #10 nationally ranked player and the #1 point guard in the class of 2015. He committed to Kentucky on November 13, 2014 live on ESPNU, becoming the third highest ranked point guard that John Calipari signed at the school. " puts me in the best position to play basketball after college," Briscoe said. "Calipari puts you on the highest stage. The last couple years, all his point guards have been in the NBA. I'm just trying to be the next one." He chose Kentucky over St. John's. He was the nation's consensus top point guard, was ranked No. 13 overall player by ESPN and Scout, No. 10 by Rivals, and No. 12 by 24/7 Sports recruiting services. He helped lead Team USA at the 2014 FIBA Americans U18 Championships to a gold medal. He was a first-team Parade All-American in 2015. He was a McDonald's All-American Game, Jordan Brand Classic, and Nike Hoop Summit game selection.
College career
As a freshman, Briscoe averaged 9.6 points and 5.3 rebounds per game. However, he struggled with his shooting particularly from outside, hitting only 14 percent of his attempts from behind the arc. Coming into his sophomore season, he worked as playing more of a point guard role. He posted 12.1 points, 5.4 rebounds, and 4.2 assists per game as a sophomore. At the conclusion of his sophomore season, Briscoe announced that he would forgo his final two years of collegiate eligibility and enter the 2017 NBA draft, becoming the fourth Kentucky Wildcat to do so.
After going undrafted in 2017 NBA draft, Briscoe joined the Philadelphia 76ers for the 2017 NBA Summer League. In six games for the 76ers, he averaged 5.5 points and 2.2 assists per game. On September 14, 2017, he signed a training camp contract with the Portland Trail Blazers. He was waived by the Trail Blazers on October 13, 2017 after appearing in six preseason games. Briscoe signed with Estonian club Kalev/Cramo. On February 16, 2018 Briscoe scored 50 points as he took home MVP honors at the Estonia/Latvia All Star Game. On June 9, 2018, Briscoe won the VTB United League Young Player of the Year award, given to the league's best player under age 23. In the 2017-18 season Briscoe averaged 18.5 points, 3.4 rebounds, 4.2 assists, and 1.6 steals in 26.7 minutes per game.
On July 6, 2018, Briscoe signed with the Orlando Magic. He made his NBA debut on October 19, 2018, recording 10 points and 3 assists off the bench in a 88–120 loss to the Charlotte Hornets. On April 4, 2019, Briscoe was waived by the Orlando Magic.
On October 25, 2019, ratiopharm Ulm of the Basketball Bundesliga announced that Briscoe had signed with them. He averaged 7.6 points, 2.6 rebounds and 2.1 assists per game for the team.
King Szczecin (2020–present)
On February 1, 2020, he has signed with King Szczecin of the PLK.
