The Belgian administration exercised authority on the basis of decrees, regulations, and by-laws, but never produced a formal constitution.

[5] The constitution was largely based on the Belgian and French legal systems, both derived from the Napoleonic Code.

It established Burundi as a constitutional monarchy with eight provinces:[9] Bubanza, Bukirasazi, Bururi, Gitega, Muramvya, Muyinga, Ngozi, and Ruyigi.

Article 6 declared that the legal system made no racial distinctions and gave Burundians equality before the law.

[13] Articles 23–50 established the Parliament of Burundi as a bicameral entity with a National Assembly and a Senate and laid out their powers.

[9] Parliament was empowered to demand the presence of government ministers at its proceedings[18] and could initiate public inquiries.

[29] Criminal trial by a board of jurors was stipulated in instances where the accused was facing capital punishment or life imprisonment.

The Supreme Court had the sole competence to try cases involving breaches of the law by ministers, deputies, and senators.

In order to be ratified, the amendment had to secure the approval of two-thirds of those voting in each chamber of Parliament as well as the agreement of the Mwami and the Crown Council.

[31] The constitution's provisions for freedom of assembly and association allowed for the continued development of a multi-party system.

[4] In accordance with the constitution, many government orders, especially those printed in the Bulletin Officiel du Burundi from 1962 to 1963, were written in both French and Kirundi.

[24] Faced with growing parliamentary opposition and the monarchy's interventions, Muhirwa gave Mwambutsa his resignation that on 7 June.

[24] From this point onward the government became increasingly subject to the maneuverings of the monarchy, and de facto lost its responsibility to Parliament.

[32] Some deputies in the National Assembly defended the Mwami's involvement in politics, citing article 57's empowerment of the monarch to choose his ministers.

[24] On 15 February 1964, the Assembly bureau penned a letter of protest to the Mwami, accusing him of violating article 61 of the constitution.

[9] On September 2 the Mwami issued an arrêté-loi that reduced the number of communes in the country from 181 to 78 and made all burgomasters appointed functionaries responsible to the crown and the government instead of locally elected officials.

Hutu politicians were infuriated by the Mwami's bypassing of the parliamentary government in issuing the decree and by removing their potential to consolidate their strength in communal elections.

On 28 September a group of Hutu members of Parliament—including the officers of both the Assembly and the Senate—signed a letter denouncing the move as unconstitutional and declared that they "absolutely refused to accept the provisions of the arrêté-loi".

[35] Faced with the difficulties of trying govern from abroad and being increasingly attracted to a comfortable life in Europe, on 24 March 1966 Mwambutsa issued a decree giving Crown Prince Charles Ndizeye "special powers to co-ordinate and control the activities of the government and the secretariats of state".

[37] In the mean time, young army officers, junior civil servants, and cadres from radical youth organisations—all mostly Tutsi—became increasingly aware of the influence which they had gained in government.

[42] Soon thereafter conflict arose between Ntare, who wished to actively rule, and the new government and its supporters, eager to implement progressive reforms without interference from the crown.

[6] In the absence of a formal legal framework, Micombero ruled by executive decree,[47] though he still abided by the constitution's guidelines for budgeting and finance.