[2] In 2016, Mayen debuted for the BA Centre of Excellence in the South East Australian Basketball League (SEABL).
[5] Mayen moved to the United States to play college basketball for the TCU Horned Frogs.
[2] He was forced to play out of position at centre early in the season as Nebraska was without Derrick Walker and Eduardo Andre for the first six games of the year.
[2] Mayen had been touted as a sharp shooter upon joining the Huskers, but finished his career shooting 33% from 3-point range with 77 total 3-pointers.
[7] Despite having a year of eligibility remaining, Mayen decided to not return to Nebraska for the 2022–23 season to begin his professional career.
[10] On 29 June 2022, Mayen signed a two-year deal with the Cairns Taipans of the National Basketball League (NBL).
[16] He left the team mid season after making the final Olympic trial group for South Sudan.
[2] Mayen was selected by the South Sudan men's national basketball team in an extended squad in the lead up to the 2024 Summer Olympics.