He received an undergraduate degree in Applied Photography in Sofia, and before the fall of Communism in 1989, worked at the National Literature Museum as a photographer.

During the June 2005 parliamentary elections, already a popular TV host, Siderov organised and led the party "Attack", named after his talk show.

Siderov reportedly espouses anti-Masonic conspiracy theories, claiming that Masons control the world through puppet regimes, international organizations, and the press.

[6] On 8 March 2013 Siderov paid tribute to the deceased president of Venezuela Hugo Chávez at the Bolivarian republic's embassy in Sofia, where he called the revolutionary an 'example for the Bulgarian patriots as a statesman'.

Siderov said that the treaty is invalid, because it was signed with Yugoslavia in 1919, a vanished state, and does not refer to the present-day Serbia or to North Macedonia and should be cancelled.

If someone asks how, I will show him: when the right of the Bulgarians to be masters in their own country became stolen, when they will be left to die in misery and lack of medicines and medical services, by being subjected to terror by Gypsy bands, who everyday [sic?]

Hundreds of thousands of chronically ill are dying right now because mob companies of the previous cabinet make dirty deals with the life and health of the Bulgarians.

Siderov and his party "Attack" were among the few Bulgarian political forces that opposed the closing of the four units of the Kozloduy Nuclear Power Plant.

[11] During a televised debate in the show Referendum on Bulgarian National Television (BNT), after arriving late, Siderov questioned the sexual orientation of IMRO leader Angel Dzhambazki, as well as Krasimir Karakachanov's property deals and alluded to what he alleged was underhanded support by the Movement for Rights and Freedoms for the nationalist IMRO party.

Gendarmerie officers arrived on scene to escort Siderov out of the studio and he was subsequently banned from appearing on the BNT by the channel's management.

Mainstream right-wing parties in Bulgaria (the UDF and the DSB) refused to back any of the candidates, despite appeals by many observers, notably by fellow conservative and European People's Party chairman Hans-Gert Pöttering, to support Parvanov (the situation was commonly compared with the way French left voters supported mainstream right-wing candidate Jacques Chirac against far-right Jean-Marie Le Pen in 2002).

He further pledged to "crush" street gangs and organized crime in Sofia in only 3 months, stating that voters were free to "have his head" if he did not fulfill this promise in time.

Adding that he thought Sofia needed its own Viktor Orbán, he further stated that he believed candidates for mayor should resign their previous posts before standing for election, as he had done with his position in the national assembly.

He was denied entry by the policemen guarding the arena and left after a long argument with the authorities, which told him that Bulgarian electoral law makes no provision for political candidates to monitor the counting process.