In the early 1840s Caxias became a member of the Reactionary Party, which evolved into the Party of Order and finally the Conservative Party. He was elected senator in 1846. The Emperor appointed him president of the Council of Ministers (prime minister) in 1856; he briefly held that office again in 1861, but fell when his party lost its parliamentary majority. Over the decades Caxias witnessed the growth and zenith of his party, then its slow decline as internal conflict divided it. In 1875, he headed a cabinet for the last time, and after years of failing health he died in May 1880.