Mamukelashvili was born in New York City and grew up in Tbilisi, Georgia after moving to the country when he was a baby. His grandmother, Ira Gabashvili, was a captain on the Soviet Union women's national basketball team. Mamukelashvili's older brother David introduced him to basketball at a young age, and Sandro grew up idolizing the Georgian player Zaza Pachulia. He was in Chicago visiting his aunt, noted pianist Eteri Andjaparidze, when the Russo-Georgian War broke out in August 2008. When he was 14 years old, Mamukelashvili moved to Biella, Italy, to attend high school. He competed on the U17, U18 and U19 teams and helped the teams to finish third place in the national finals. Mamukelashvili said that moving to Italy was difficult but his club and head coach Federico Danna made everything possible for him. In 2016, he moved to the United States to attend basketball powerhouse Montverde Academy, where he played alongside New York Knicks player RJ Barrett. While at Montverde, Pachulia became a mentor to the young man and introduced him to several NBA players such as Stephen Curry. Mamukelashvili scored 11 points in a 72–45 win over Greensboro Day School to help Montverde reach the finals of the DICK’S Sporting Goods High School Nationals. In April 2017, Mamukelashvili signed with Seton Hall over offers from USC, South Carolina, and Vanderbilt among others. He chose the Pirates because his high school coach Kevin Boyle had a good relationship with Seton Hall coach Kevin Willard and his brother David lives nearby. He is fluent in English, Georgian, Russian, and Italian.
College career
As a freshman, Mamukelashvili averaged 2.6 points, 1.9 rebounds and 0.5 blocks per game and helped the Pirates reach the second round of the NCAA Tournament. His best game as a freshman came against Xavier on February 14, 2018, when he scored 17 points and grabbed seven rebounds. As a sophomore, he averaged 8.9 points and 7.8 rebounds per game. On December 19, Mamukelashvili scored a season-high 23 points on 8-of-11 shooting and had eight rebounds in a 90–76 win over Sacred Heart. Following his sophomore season, Mamukelashvili worked with Pachulia at his Academy in Tbilisi to expand his game, adding a jump stop and improving his three-point shooting. On November 29, 2019, Mamukelashvili scored 18 points on 7-of-10 shooting and had six rebounds in an 84–76 win over Iowa State in the Bahamas. During the Battle 4 Atlantis tournament, Mamukelashvili averaged 14 points, 5.7 rebounds and 2.0 assists per game while making 61 percent of his shots from the field and 60 percent from behind the arc. He fractured his right wrist in a game against Iowa State on December 8 and missed several weeks. On January 29, 2020, he returned to the court, playing five minutes in a 64–57 win over DePaul. On February 19, with his father Zurab in attendance for the first time in two years, Mamukelashvili scored 15 points and had six rebounds, hitting the game-winning shot on an inbounds pass with 0.6 seconds remaining in a 74–72 win over Butler. He had a career-high 26 points on February 29, in an 88–79 win over Marquette. Mamukelashvili averaged 11.9 points and 6.0 rebounds per game as a junior. After the season, he declared for the 2020 NBA draft but did not hire an agent, signaling high potential to return to Seton Hall for his senior campaign.
