On August 26, 2018, Mullings scored his first collegiate goals, netting a brace in a 2-0 victory over the Presbyterian Blue Hose, subsequently earning Atlantic Sun Conference Player of the Week honours.[6][7] At the end of his freshman season, he was named ASUN Freshman of the Year and was named to the All ASUN-Freshman Team, the ASUN All-Conference First Team, and the All-Atlantic Region Second Team.[8][9] He was also named the school's Scholar-Athlete of the Month for January.[10]
In his sophomore season, he recorded two braces,[11][12] and earned back-to-back ASUN Player of the Week honours in October.[13][14] At the end of the season, he was named an ASUN First Team All-Conference, the All-Atlantic Region Third Team, and the ASUN All-Tournament Team.[15][16][17] At the end of the school year, he was named the school's co-Most Outstanding Athlete and was named to the ASUN All-Decade Team.[18][19]
Ahead of his junior season, he was named the ASUN Preseason Player of the Year and was named to the Preseason All-Conference Team.[20] On March 6, 2021, he scored a brace against the Jacksonville Dolphins, earning College Soccer News Team of the Week honours.[21][22] At the end of the season, he was named ASUN Player of the Year and selected to the ASUN All-Conference First Team and the ASUN All-Tournament Team.[23][17]
Ahead of his senior season, he was again named to the ASUN Preseason All-Conference team.[24] After scoring back-to-back braces in mid-September,[25][26] he again won ASUN Player of the Week honours.[27] At the end of the season, he was once again named to the ASUN All-Conference First Team and was named to the All-Atlantic Region Second Team.[28][29] He finished his time at FGCU with 28 goals and 63 points in 57 games, ranking second in the school's all-time goals and points totals.[30]
In January 2022, Mullings was selected in the first round (20th overall) of the 2022 MLS SuperDraft by the New York Red Bulls.[32][33] In March 2022, he signed a contract with their second team, New York Red Bulls II, in the USL Championship.[34] He made his professional debut on March 16, 2022, starting in a 1–0 win over Atlanta United 2[35] and was also named the team captain that season.[36] On July 30, 2022, he featured for the first team in a friendly against Spanish club FC Barcelona.[37] On August 9, 2022, Mullings scored his first professional goal, netting the winning goal for New York in a 2-1 victory over Atlanta United 2.[38] In late August 2022, he was named to the USL Championship Team of the Week for the first time for Week 24 of the season.[39] In February 2023, he re-signed with the second team, ahead of their debut season in MLS Next Pro.[40][41] Mullings signed a short-term loan with the first team on May 17, 2023.[42] He made his MLS debut the same day against Toronto FC, as a second-half substitution in a scoreless draw.[43] He later signed an additional three short-terms loans in the remainder of the month, fulfilling his maximum of four.[44][45][46] In August 2023, he was awarded the MLS Next Pro Goal of the Matchday for his goal on August 6 against New England Revolution II.[47]
