Posthumus attended River East Collegiate, a high school located in Winnipeg, Manitoba in Canada.

He was considered one of the top high school basketball players in the country as a senior, averaging 39 points, 25 rebounds, and 7 blocks.

[1] Posthumus returned to Morehead State for his final college season and averaged 9.6 points off 51% shooting along with 10.9 rebounds per game which was the second highest in the nation.

He also posted 10 double-doubles and following the season Posthumus earned College Sports Madness All-Ohio Valley Conference (OVC) honours and gained fame back in Canada.

On August 1, 2014, Posthumus signed his first professional contract with Levanga Hokkaido of the Japan Basketball League (JBL).

[2] Posthumus made his pro debut on October 11, 2014, against the Mitsubishi Diamond Dolphins, scoring 16 points and posting 13 rebounds.

[3] On January 9, 2015, Posthumus inked a contract with the Mississauga Power of the National Basketball League of Canada (NBL).

[12] As a redshirt sophomore, while attending Howard College, Posthumus was named an Academic All-American and a member of the Dean's List.