After entering the Roman Curia, in the Secretariat of State, in 1904, Micara was named secretary of the nunciature to Argentina in 1909.

He received his episcopal consecration on the following 8 August from Cardinal Pietro Gasparri, with Bishops Antonio Valbonesi and Karl Kašpar serving as co-consecrators, in the chapel of the Bohemian College in Rome.

Pope Pius XII named Micara Cardinal-Priest of Santa Maria sopra Minerva in the consistory of 18 February 1946, and then Bishop of Velletri-Segni on 13 June.

He was called the "Grand Elector" among the Curia because of his influential role in securing the votes of conservative cardinals' for Pope Paul, with whom he was friends, in the latter conclave.

He died on 11 March 1965 after a long illness[2] in Rome, at age 85, and was buried in the basilica of Santa Maria sopra Minerva.