Oni made his junior season debut on November 9, 2018, scoring 16 points in a 76–59 win over California at the Pac-12 China Game held in Shanghai.
On November 21, he posted his first double-double of the season, leading his team with 18 points and 10 rebounds in a 79–70 loss to Vermont.
On December 1, Oni scored 29 points and was named game MVP in a 77–73 victory over Miami (Florida) at the Hoophall Miami Invitational.
He erupted for 31 points, 9 rebounds, and 4 assists, leading his team in each category, on February 2, 2019 in an 89–68 win over Dartmouth.
Oni was the first Yale player to record a 30-point game since Anthony Dallier in 2017.
In his next game, a 74–60 victory over Princeton, he posted a career-high 35 points, 12 rebounds, and 3 blocks.
Oni scored the most single-game points in school history since Greg Mangano in 2012.
He delivered another strong performance on March 1, when he scored 30 points—shooting 9-of-11 from the field—to help Yale defeat Cornell, 88–65, and clinch a spot in the 2019 Ivy league Tournament.
By the end of the regular season, Oni was averaging a team-best 17.4 points, 6.3 rebounds, and 3.6 assists per game.
He was named Ivy League Player of the Year, becoming the third Yale player to win the award.

In his junior season, Oni frequently attracted attention from NBA scouts, who visited all of his games to see him play.
He was considered a top-50 prospect for the 2019 NBA draft and became the first Ivy League player to be drafted since 1995.
In December 2018, Duke head coach Mike Krzyzewski predicted that he would be a first-round pick.
Oni made his junior season debut on November 9, 2018, scoring 16 points in a 76–59 win over California at the Pac-12 China Game held in Shanghai. On November 21, he posted his first double-double of the season, leading his team with 18 points and 10 rebounds in a 79–70 loss to Vermont. On December 1, Oni scored 29 points and was named game MVP in a 77–73 victory over Miami (Florida) at the Hoophall Miami Invitational. He erupted for 31 points, 9 rebounds, and 4 assists, leading his team in each category, on February 2, 2019 in an 89–68 win over Dartmouth. Oni was the first Yale player to record a 30-point game since Anthony Dallier in 2017. In his next game, a 74–60 victory over Princeton, he posted a career-high 35 points, 12 rebounds, and 3 blocks. Oni scored the most single-game points in school history since Greg Mangano in 2012. He delivered another strong performance on March 1, when he scored 30 points—shooting 9-of-11 from the field—to help Yale defeat Cornell, 88–65, and clinch a spot in the 2019 Ivy league Tournament. By the end of the regular season, Oni was averaging a team-best 17.4 points, 6.3 rebounds, and 3.6 assists per game. He was named Ivy League Player of the Year, becoming the third Yale player to win the award.
In his junior season, Oni frequently attracted attention from NBA scouts, who visited all of his games to see him play. He was considered a top-50 prospect for the 2019 NBA draft and became the first Ivy League player to be drafted since 1995. In December 2018, Duke head coach Mike Krzyzewski predicted that he would be a first-round pick.
Miye Oni