Mensah has made appearances for various national youth teams of Denmark while at Viborg, gaining 26 total caps in which he scored four goals.

[9] After Viborg FF reached promotion to the Superliga in 2013, Mensah signed another two-year contract extension keeping him in his hometown club until 30 June 2015.

[11] On 2 March 2015, Mensah made his debut for Esbjerg in a Danish Superliga match against AaB, coming in as a 72nd-minute substitute for Mohammed Fellah.

[14] Due to a groin injury, he made his debut months later on 10 April 2017, coming off the bench for Kamil Wilczek in the 74th minute during a 1–0 loss to Copenhagen in a derby at Brøndby Stadium.

[17] In the final match of the 2017–18 season, Mensah tore his anterior cruciate ligament, requiring knee surgery that sidelined him for seven to nine months.

[1] Due to Anthony Jung's poor form at left back, Mensah was utilised in this position too in the 2018–19 season with great success.

[22] He made his comeback on 10 April 2023, 13 months after suffering the knee injury, replacing Blas Riveros in the 64th minute of a 2–1 loss to Nordsjælland.