After his ordination he was appointed curate in Hütteldorf, and later professor of church history and canon law at Salzburg, where Friedrich Prince Schwarzenberg, director of the Oriental Academy at Vienna, was among his pupils.

In January 1849 Cardinal Schwarzenberg named his former teacher Prince-Bishop of Sekkau, "in recognition of his distinguished qualities, knowledge, and services".

He also fostered religious associations, and put an end to the intrigues of the Rongeaner, although important business detained him for the most part in Vienna.

The negotiations were long and troublesome; during them Rauscher was named Prince-Archbishop of Vienna, and made his solemn entry into the Cathedral of St. Stephen on 15 August 1853.

By 1 January 1857, ecclesiastical courts, for which Rauscher composed the instructions (Instructio pro indiciis ecclesiasticis), were established in all the episcopal sees.

The decrees of the Viennese Council of 1858, directed by Rauscher and ratified by Rome, served as an important form of clerical life and ecclesiastical activity.

When the House of Delegates demanded the removal of the religious orders from the penitentiaries, hospitals, and other state institutions, he declared in the House of Peers: Since 1859 no effort of artificial agitation has been spared to open a campaign against defenceless women, who ask of this earthly life only necessities, and serve their fellow-creatures in privations and discomforts.

However, Rauscher immediately obtained from the emperor the annulment of the sentence and of the consequences which it entailed with respect to civil rights and relations.

At the first real session of the council (the General Congregation of 28 December) he delivered the first address, and twice spoke against the opportuneness of a universal catechism; the needs and the degrees of culture of the individual peoples were too different.

As to the question which finally most strongly stirred the minds of those in and outside the council, that of the infallibility of the pope teaching ex cathedra, Rauscher was the leader of the bishops who combatted the expediency of the definition.

His work, "Observationes quædam de infallibilitatis ecclesiæ subjecto", appeared at Naples, and was reprinted at Vienna; the author later explained that it "was especially intended to emphasize the fact that the proposed decision would afford parties hostile to the Church those subterfuges of which they were in need".