From 1943, he was a member of the BRP (so-called) and commander of the "Bratya Krastini" detachment, which grew into the "Chepinets" partisan brigade.
In 1944, he participated in the Second World War against Nazi Germany, as an assistant company commander in the 27th Infantry Regiment (from September to December 1944).
From November 5, 1962, Lieutenant-General Semerdzhiev was a candidate member of the Central Committee of the BKP and first deputy minister of national defense.
In Bulgaria, these events are associated with the date November 10, 1989, when Todor Zhivkov was released from the position of general secretary in the party (de facto head of state of the country).On December 27, 1989, Gen. Atanas Semerdzhiev was appointed Minister of Internal Affairs in the government of Georgi Atanasov (June 1986 – February 1990).
From January 29, 1990, with a top secret memo of particular importance, Gen. Atanas Semerdzhiev orders the files of the State Security (DS) agent apparatus to be purged.
A few years later, a case was filed against General Semerdzhiev in connection with this order of his, issued in his capacity as Minister of Internal Affairs of Bulgaria.
In August 1990, after the resignation of Petar Mladenov, as a result of a compromise political agreement between the ruling BSP and the opposition, which allowed Atanas Semerdzhiev to be elected vice president, and Zhelyu Zhelev, the leader of the opposition Union of Democratic Forces, to be president.
7 of July 19, 2007, of the Commission for disclosure of documents and for declaring the affiliation of Bulgarian citizens to the State Security and Intelligence Services of the BNA, the agent activity of Atanas Georgiev Semerdzhiev in his capacity as the content of a report under the name " The Nightingale".
A trial begins on accusations that, in his capacity as Minister of the Interior, Atanas Semerdzhiev ordered the destruction of 134,102 intelligence files.
For the destroyed cases, prepare formalized replacement cards without names, but only with pseudonyms and a registration number, to be microfilmed.
The restructuring to create a reserve fund in which to preserve all important documents under the direction of gen. Nanka Serkejieva as head of the Archives Department.
Semerdzhiev was placed under house arrest, which lasted for two and a half years, after which the measure ended being replaced by signature and money guarantee.
They appealed and the Supreme Court established that the sentences pronounced were the result of political intent and were legally untenable.