After service in the Peninsular War, Bentinck was appointed commander of British troops in Sicily. A Whig, Bentinck used this position to meddle in internal Sicilian affairs, effecting the King's withdrawal from government in favour of his son, the Crown Prince, the reactionary Queen's disgrace, and an attempt to devise a constitutional government for the troubled island, all of which ultimately ended in failure. In 1814, Bentinck landed with British and Sicilian troops at Genoa, and commenced to make liberal proclamations of a new order in Italy which embarrassed the British government (which intended to give much of Italy to Austria), and led, once again, to his recall in 1815.
Bentinck engaged in an extensive range of cost-cutting measures, earning the lasting enmity of many military men whose wages were cut. Although his financial management of India was quite impressive, his modernising projects also included a policy of westernisation, influenced by the Utilitarianism of Jeremy Bentham and James Mill, which was more controversial. Reforming the court system, he made English, rather than Persian, the language of the higher courts and encouraged western-style education for Indians in order to provide more educated Indians for service in the British bureaucracy.
Bentinck also took steps to suppress sati, the death of a widow on her husband's funeral pyre, and other Indian customs which the British viewed as barbaric. Although his reforms met little resistance among native Indians at the time, it has been argued that they brought on dissatisfaction which ultimately led to the great Mutiny of 1857. His reputation for ruthless financial efficiency and disregard for Indian culture led to the much-repeated story that he had once planned to demolish the Taj Mahal and sell off the marble. According to Bentinck's biographer John Rosselli, the story arose from Bentinck's fund-raising sale of discarded marble from Agra Fort and of the metal from a famous but obsolete Agra cannon.
The department of Manuscripts and Special Collections, The University of Nottingham holds the personal papers and correspondence of Lord William Bentinck (Pw J), as part of the Portland (Welbeck) Collection.