Masidi entered the State Public Service in 1977 as a legal adviser and prosecutor at the Forestry Department.

[5] He was admitted as an Advocate and Solicitor of the High Court of Sabah and Sarawak in 1980, the same year he was appointed as Tuaran District Officer.

[5] He was transferred to Sandakan as the town's municipal council president in 1982 before being promoted as Permanent Secretary of Ministry of Culture, Youth and Sports in 1984.

[6] Masidi joined politics in 2004 as he was nominated by United Malays National Organisation (UMNO) as candidate for Karanaan state constituency.

He is currently serving the fifth term in Karanaan following his victory in the 16th state election under the banner of Malaysian United Indigenous Party (BERSATU).