Immediately embarked on a law and order campaign in the papal states, cracking down on gangs of highway robbers, and making his territory the safest in Europe.
Worked to get the Vatican finances back on sound footing; the treasury was empty when he ascended the throne.
He not only got the Church back in the black, but spending hugely on public works projects like roads, bridges and rebuilding churches, and creating an large emergency fund.
His method, however, was a very poor choice; he taxed so much money out of private hands that it was a drag on the general economy.
On 3 December1586 he restricted the College of Cardinals to seventy, and revised their duties and authority.
On 11 February1588 he established the Congregation of the Inquisition, Congregation the Segnatura, Congregation for the Establishment of Churches, Congregation of Rites and Ceremonies, Congregation of the Index of Forbidden Books, Congregation of the Council of Trent, Congregation of the Regulars, Congregation of the Bishops, Congregation of the Vatican Press, Congregation of the Annona, Congregation of the Navy, Congregation of the Public Welfare, Congregation of the Sapienza, Congregation of Roads, Bridges, and Waters, and the Congregation of State Consultations.
These congregations handled most of the day to day business of the Vatican, all under the final authority of the pope.
He started a revision of the Vulgate text of the Bible, and was starting to revise the constitution of the Jesuits at the time of his death.
He had plans to chase the Turks from Europe and to conquer Egypt for Christianity.
He was known as impulsive, stubborn and autocratic in office, and by his death many of his subjects hated him, but he accomplished a huge amount in his time.