[6] In the 2016 summer, Porter joined Mokan Elite on the Nike Elite Youth Basketball League (EYBL) averaging 26.2 points and 11.5 rebounds per game leading them to the Nike EYBL Peach Jam championship and was named Co-MVP alongside teammate and future NBA player Trae Young.

[7] In his senior season, Porter averaged 36.2 points and 13.6 rebounds as he helped his high school team earn a perfect 29–0 record and win the Washington Class 3A State Championship.

[3][2] On March 29, 2017, Porter was named MVP at the McDonald's All-American Game leading the West in a 109–107 win over the East team.

[18] Porter would also play in the first round of the 2018 NCAA Division I men's basketball tournament, where the team lost to Florida State.

On March 27, Porter announced his intention to forgo his final three seasons of collegiate eligibility and declared for the 2018 NBA draft.

[23] On July 19, 2018, the Nuggets announced that Porter had undergone a second back surgery[24] and subsequently missed the entire season.

On October 31, 2019, Porter made his debut in the NBA, coming off the bench with fifteen points, four rebounds, and an assist in a 107–122 loss to the New Orleans Pelicans.

[25] On December 29, he made his first career start in the NBA, finishing with 19 points, along with six rebounds and an assist in 26 minutes in a 120–115 win over the Sacramento Kings.

[27] On August 4, 2020, returning from the suspension of the season due to the COVID-19 pandemic, Porter Jr. led the Nuggets to their first victory in the Orlando bubble, scoring a then career-high 37 points in route to a 121–113 overtime win over Oklahoma City Thunder.

[30] He was expected to be the secondary scoring option behind Nikola Jokić while Jamal Murray continued to recover from a torn ACL.

[42] In April 2024, his younger brother Coban was sentenced to six years in prison for killing a woman while driving under the influence of alcohol.