The Chief Secretary for Ireland was a key political office in the British administration in Ireland. Nominally subordinate to the Lord Lieutenant, and officially the "Chief Secretary to the Lord Lieutenant", from the early 19th century until the end of British rule he was effectively the government minister with responsibility for governing Ireland, roughly equivalent to the role of a Secretary of State, such as the similar role of Secretary of State for Scotland. Usually it was the Chief Secretary, rather than the Lord Lieutenant, who sat in the British Cabinet. The Chief Secretary was ex officio President of the Local Government Board for Ireland from its creation in 1872.

Dublin Castle was the centre of the government of Ireland under English and later British rule. "Dublin Castle" is used metonymically to describe British rule in Ireland. The Castle held only the executive branch of government and the Privy Council of Ireland, both appointed by the British government. The Castle did not hold the judicial branch, which was centred on the Four Courts, or the legislature, which met at College Green until the Act of Union 1800, and thereafter at Westminster.