Royal power was exercised on his behalf by a regency council led by Simeon's uncle Kiril, Prince of Preslav, General Nikola Mihov and prime minister, Bogdan Filov.

As of 15 January 2025[update], Simeon is one of only two living men who were heads of state during World War II, along with the 14th Dalai Lama, although both held mostly symbolic roles in their government's position.

Following his birth, Boris III sent an air force officer to the Jordan River to obtain water for Simeon's baptism in the Orthodox faith.

[4][5] Since Simeon was only six years old, his uncle Prince Kiril, Prime Minister Bogdan Filov, and Lt. General Nikola Mihov of the Bulgarian Army were appointed regents.

[6] Under his father, Bulgaria joined the Axis powers in World War II but managed to preserve diplomatic relations with the Soviet Union.

[6] The royal family — Queen Giovanna, Simeon, and his sister Maria-Louisa — remained at Vrana Palace, near Sofia, while three new regents were appointed, all Communists (Todor Pavlov, Venelin Ganev and Tsvetko Boboshevski).

[10] However, these social sentiments gradually disappeared after his premiership, with Simeon making moves to take back large areas or real estate property in Bulgaria that was under the monarchy's governance before 1945.

"[11] Simeon promised that in 800 days the Bulgarian people would feel tangible positive effects of his government and would enjoy significantly higher standards of living.

[12] NMSP won a large victory in the parliamentary elections held on 17 June 2001, capturing 120 of the 240 seats in Parliament and defeating the two main pre-existing political parties.

Simeon was sworn in as Prime Minister of Bulgaria on 24 July, forming a coalition with the ethnic Turkish-led party, Movement for Rights and Freedoms (MRF).

Since his return to Bulgaria, however, Simeon has consistently avoided revealing his views on the restoration of the Bulgarian monarchy, notwithstanding the original name of his party.

Simeon wrote an autobiography in French under the title Siméon II de Bulgarie, un destin singulier that was released in Bulgaria on 28 October 2014.