On 24th February, 1966 following the coup-d'tat which overthrew the CPP government, E.R.T. Madjitey was released from detention and was appointed Ghana's High Commissioner to Pakistan by the National Liberation Council. E.R.T. Madjitey held this position until 1969 when upon the request from the people of Krobo, he left the Diplomatic Service and contested in the 1969 elections on the ticket of K. A. Gbedemah's National Alliance of Liberals winning in the Manya Krobo constituency and becoming its member of Parliament.
Owing to a void created by the disqualification of K. A. Gbedemah from holding public office, the various opposition parties united into the Justice Party. E.R.T. Madjitey was appointed leader of the Justice Party thus becoming leader of the parliamentary opposition in the second Republic.
In January 1972 parliament was dissolved and he lost this office when the Ghana Armed Forces in one of the many tumultuous coup detats [under a Colonel] overthrew the second Republican government of Professor Kofi Abrefa Busia.
In 1977 when Colonel Acheampong [later self promoted to General] decided to overturn Ghana's historical democratic process with the concept of a socialist style government dubbed UNIGOV, E.R.T. Madjitey together with Messrs William Ofori-Atta, Harry Sawyer, Victor Owusu, Professor Adu Boahene, General A. A. Afrifa, G.K. Agama, Sam Okudjeto, Obed Asamoah and others constituted a small anti-UNIGOV group called the Peoples Movement for Freedom and Justice to resist this move after a 1977 referendum widely believed to have been rigged. Madjitey and some members of the PMFJ were arrested and put in detention. Gen. Acheampong however, became so unpopular that in 1978 he was ousted by his colleagues on the Supreme Military Council in a palace coup and replaced by General F.W.K. Akuffo (July 1978). General Akuffo subsequently decided to return the nation to constitutional rule and therefore set up a Constitutional Drafting Commission and released the political prisoners.
Between 1977 and 1978, E.R.T. Madjitey served as a member of the Constitutional Drafting Commission which drew up the Third Republican Constitution of Ghana. He was also a member of the 1979 Constituent Assembly to defend and ratify the Draft Constitution. When the SMC under Gen. Akuffo lifted the ban on political activities. Madjitey helped found the Popular Front Party led by Victor Owusu in 1979 which became the main opposition party in the Third Republic. He was also a founding member of the New Patriotic Party, which was again the main opposition party in the first two parliaments of the Fourth Republic but won power in December 2000 under John Adjekum Kufuor.