Rainilaiarivony emerged from the Hova political class that had acquired increasing influence in the army, administration, and commercial life of the Merina kingdom. In July 1864, he replaced his brother Rainivoninahitriniony as prime minister and combined that office with command of the army. Holding both positions gave him control over the principal political and military instruments of the state.

Rainilaiarivony’s authority expanded through his marriage to Queen Rasoherina, despite the difference in their ages. The union helped make him the most powerful man in Madagascar, and his later marriage to the succeeding queen reinforced his position. He thus became, in practice, an uncrowned king, while the Hova oligarchy increasingly exercised the authority that had traditionally belonged to the monarch and the Andriana group.

The administrative system under Rainilaiarivony centralized final judicial decisions in the office of the prime minister, even when cases were heard in village courts or the superior courts at the capital. He also stood at the center of military modernization, including the creation of a large professional army and the campaigns that extended central government control over the Bara in 1873. His political and economic influence reached beyond administration: the passage identifies him as an active trader with a personal bank account in Mauritius used to purchase luxury goods.