Like many other peasant party leaders in Poland, Hungary, and Bulgaria in 1945–1947, Petkov was tried and executed soon after postwar Soviet control was established in his country.

[1] State Department emissary, Mark Ethridge, sent to Bulgaria in 1945 to report on conditions to President Truman, called him "the bravest man I've ever known.

After the coup of 9 June 1923 when the BZNS government under Aleksandar Stamboliyski was removed from office, Nikola Petkov resigned and stayed in France where he worked as a journalist.

In 1929 he returned to Bulgaria and became an editor of the newspapers Zemya (1931–1932) and Zemedelsko zname – an organ of Bulgarian Agrarian People's Union "Aleksandar Stamboliyski" (1932–1933).

He prepared and published a book on Aleksandar Stamboliyski in which he made political analysis and characteristics on the personality and the activities of the agrarian leader.

[3] After a show trial in which the defence was denied the rights to legal representation or to present evidence, he was found guilty of espionage and sentenced to death on 16 August that year.

The Bulgarian secret police arranged for a false confession to be publicly printed after Petkov's death, but it was so obviously faked that the move quickly became an embarrassment and ceased to be mentioned by the authorities.