In 1810, he succeeded his father Andrianimpoinimerina as king of Merina, a small area in the central plateau of the island, around Antananarivo. Am ambitious ruler, he first took over the Betsileo area in the southern part of the central highlands, then the Sakalava. By playing off competing British and French interests, he acquired British aid for his military, which he then used to conquer most of the rest of the island by 1824.
Radama also encouraged social and political change; he organized a cabinet, and invited the Protestant London Missionary Society to establish schools and churches. The Society also brought a printing press, and devised a written form of the Malagasy language.
He officially abolished the slave trade in 1817, although slave-dealing continued.
Radama was succeeded by his wife, Queen Ranavalona I.