The Conservative government of the United Kingdom of Great Britain and Ireland that began in 1866, and ended in 1868, consisted of the two ministries: the Third Derby ministry, and then the First Disraeli ministry.
Lord Derby became Prime Minister for the third time, after the fall of Lord Russell's Liberal government, in 1866. His Chancellor of the Exchequer, Benjamin Disraeli, was instrumental in passing the Second Reform Act in 1867.
After the parliamentary session, which produced the Second Reform Bill, Disraeli's eventual assumption of the leadership of the Conservative Party was all but assured. While he was still opposed by elements of the party's right wing (most notably the Marquess of Salisbury, himself a future Prime Minister), his role in securing the passage of the bill, in particular his showing against William Ewart Gladstone, had won him the adulation of a wide base of the parliamentary party. The only unknown was the health of the Earl of Derby, still very much Prime Minister, Conservative leader, and Disraeli's colleague.
Derby's health, however, had been in decline for some time, and he finally resigned in February and advised Queen Victoria to send for Disraeli. Thus on 27 February 1868 Benjamin Disraeli became Prime Minister of the United Kingdom. He reportedly said of the event later, "I have climbed to the top of the greasy pole." However, the Conservatives were still a minority in the House of Commons, and the enaction of the Reform Bill required the calling of new election. Disraeli's term as Prime Minister would therefore be fairly short, unless the Conservatives managed to win the general election.