Son of the Reichsvizekanzler in Vienna, Colloredo was educated in Vienna and Rome, became a Salzburg canon in 1747, and Prince-archbishop of Salzburg on 14 March 1772. This election was bitterly controversial - Salzburg`s political position was sensitive, and both Austria and Bavaria had favourite candidates. Colloredo was Austria`s choice: Bavaria`s was Ferdinand Christoph von Waldburg-Zeil, the popular dean of Salzburg.
Colloredo inherited huge debts from his predecessor Schrattenbach, and immediately tried to reduce them. He also began to implement his Enlightenment reforms, a task of bewildering enormity, since Schrattenbach had been ultra-conservative. Colloredo had to establish like-minded people in each institution—ecclesiastical, educational, legal, medical, fiscal, administrative, and publicistic—and persuade the reluctant populace to change its entire mentality. Colloredo ruled Salzburg for thirty years and was ultimately successful in his main aims, but the struggle was a perpetual one. He was hampered by shortage of funds and his inability to be popular, as he was both sarcastic and misanthropic – a typical view was represented by the slogan `Enlightenment and love of mankind on paper`. Colloredo was no puppet of Vienna`s. He drew on Enlightenment models from Protestant Germany, Rhineland-Franconia, Italy, The Austrian Netherlands, Swabia, and Bavaria, as well as Austria. Recognizing and defending Salzburg`s historical position as a Catholic state, he pursued his reforms within the broad structures of the Church, attracting European-wide admiration for his efforts.
Colloredo`s pastoral letter of 1782 shunned outward pomp, espousing simplicity and tolerance of other creeds. Pilgrimages and superstitious practices were banned, processions were restricted, church decoration was limited, musical settings of the Mass were shortened, and sacred German hymns introduced. Purely instrumental music was discouraged in church. These changes led to deep resentment, and Colloredo and the architect of the pastoral letter, Johann Michael Bönike, were called `secret Lutherans`.
In 1775 Colloredo opened a public theatre, and in 1778 the university theatre was closed depriving Salzburg musicians of an important outlet for musical performance. The church music reforms represented another restriction, and Colloredo`s strict financial policies also limited musical opportunities at court.
Mozart was given his first Salzburg salary under Colloredo. Nevertheless, the Mozarts strongly disliked him. Travel leave was difficult to obtain, and they complained that extra presents of money for compositions were stingy, and that Colloredo was scathing about Mozart`s abilities. After Mozart`s second resignation in 1781, Leopold continued to bemoan the failure to replace musicians who had left or died, and the consequent shambles in the court music. Colloredo was himself a music lover as well as an intellectual, and sometimes played the violin in the court orchestra, but he had larger concerns.
In 1800 Colloredo had to flee Salzburg, because of the turbulent political situation in Europe. He resigned as head of state in 1803 and Salzburg was secularized.

H. Dopsch and H. Spatzenegger (eds.), Geschichte Salzburgs: Stadt und Land I:1 (Salzburg, 1988) C. Eisen, `Salzburg under Church Rule`, in The Classical Era. From the 1740s to the End of the 18th Century, ed. N. Zaslaw (London, 1989), 166-187