A private secretary (PS) is a civil servant in a governmental department or ministry, responsible to a secretary of state or minister; or a public servant in a royal household, responsible to a member of the royal family.

The role exists in the civil service of the United Kingdom and several Commonwealth countries including Australia, India and New Zealand as well as other countries influenced by the Westminster system. A private secretary is normally of middle management level; however, as the key official responsible for disseminating ministers' decisions and guidance on matters of policy, and as their gatekeeper, the role is of considerably greater significance than their grade would suggest. Depending on the status of the political principal the official works for, they may be aided by an assistant private secretary (APS), or head a private office.

A principal private secretary, or senior private secretary, is a senior civil servant who runs a cabinet minister's private office. A similar role to a principal private secretary in the United States federal government would be chief of staff.

The private secretary to the sovereign is viewed as being equivalent to a permanent secretary, the head of a government department.