In 1871, he was elected deputy for Sarthe. A monarchist, he was a member of the republican-conservative Target group which participated in the overthrow of Adolphe Thiers in 1873. A supporter of the Duke of Broglie's two governments, Caillaux entered government himself in May 1874, as Minister of Public Works in Ernest Courtot de Cissey's government, remaining in post until 1876 in Louis Buffet and Jules Dufaure's governments. As minister, he was a supporter of the railway companies and took a special interest in the improvement of the Loire basin.
Caillaux was elected a senator for Sarthe in January 1876, the last of three on the Union conservatrice list. from May to November 1877, he was Minister of Finance under Broglie.[1][2] In 1882, he was defeated in the senatorial elections by the republicans, and abandoned national politics in favour of local politics in Sarthe.