Percy Clinton Sydney Smythe, 6th Viscount Strangford GCB GCH (31 August 1780 – 29 May 1855) was a British diplomat.

[2] Smythe was educated at Harrow and graduated from Trinity College, Dublin in 1800, entered the diplomatic service, and in the following year succeeded to the title of Viscount Strangford in the Peerage of Ireland.

[1] He had literary tastes, and in 1803 published Poems from the Portuguese of Camoēns, with Remarks and Notes, Byron at this time describing him as "Hibernian Strangford".

Sworn of the Privy Council in March 1808, Lord Strangford was appointed 16 April envoy-extraordinary to the Portuguese court in Brazil, and shortly sailed to join the Prince Regent (the future John VI) and to advocate for British interests.

[10] His diplomatic career went into decline after he was caught falsifying dispatches to the British government and revealing confidential documents to the Austrian ambassador in St Petersburg.

On his death on 29 May 1855, he was succeeded by his eldest son George Smythe, 7th Viscount Strangford, who was an active figure in the Young England movement of the early 1840s.

A window in his family chapel in St. Mary's Church, Ashford, Kent, commemorates him, mentioning the monarchs whom he served and the countries to which he was dispatched.