Adjei Mensah was elected as the member of parliament for the Techiman North constituency in the 2000 Ghanaian general elections. He was elected on the ticket of the National Democratic Congress. His constituency was a part of the 7 parliamentary seats out of 21 seats won by the National Democratic Congress in that election for the Brong Ahafo Region. The National Democratic Congress won a minority total of 92 parliamentary seats out of 200 seats in the 3rd parliament of the 4th republic of Ghana. He was elected with 9,830 votes out of 20,362 total valid votes cast. This was equivalent to 49.8% of the total valid votes cast. He was elected over Isaac Osei-Antwi of the New Patriotic Party, Thomas Oti of the National Reform Party, James Stephen Fordwour of United Ghana Movement and Yeboah Godfrey of the Convention People's Party. These obtained 10,563, 533, 529 and 177votes respectively out of the total valid votes cast. These were equivalent to 39.5%, 2.0%, 2.0% and 0.7% respectively of total valid votes cast. The electorates in that election of 2000 in the Techiman North Constituency exhibited a "skirt and blouse" kind of voting as the presidential candidate elected in that constituency was John Kuffour of the opposition New Patriotic Party.
