The Marquess of Downshire is a marquess in the Peerage of Ireland. The title was created in 1789 for Wills Hill, 1st Earl of Hillsborough, a former secretary of state.

The Marquess holds the subsidiary titles of Earl of Hillsborough (Peerage of Great Britain, 1772), Earl of Hillsborough (Peerage of Ireland, 1751), Viscount Fairford (Peerage of Great Britain, 1772), Viscount Hillsborough (Peerage of Ireland, 1717), Viscount Kilwarlin (Peerage of Ireland, 1751), Baron Harwich (Peerage of Great Britain, 1756), and Baron Hill of Kilwarlin (Peerage of Ireland, 1717).

Prior to the passage of the House of Lords Act 1999 the Marquess sat in the House of Lords as Earl of Hillsborough.

Viscounts Hillsborough (1717)

• Trevor Hill, 1st Viscount Hillsborough (1693-1742)
• Wills Hill, 2nd Viscount Hillsborough (1718-1793) (became Marquess of Downshire in 1793)

Marquesses of Downshire (1789)

• Wills Hill, 1st Marquess of Downshire (1718-1793)
• Arthur Hill, 2nd Marquess of Downshire (1753-1801)
• Arthur Blundell Sandys Trumbull Hill, 3rd Marquess of Downshire (1788-1845)
• Arthur Wills Blundell Sandys Trumbull Windsor Hill, 4th Marquess of Downshire (1812-1868)
• Arthur Wills Blundell Trumbull Sandys Roden Hill, 5th Marquess of Downshire (1844-1874)
• Arthur Wills John Wellington Trumbull Blundell Hill, 6th Marquess of Downshire (1871-1918)
• Arthur Wills Percy Wellington Blundell Trumbull Hill, 7th Marquess of Downshire (1894-1989)
• Arthur Robin Ian Hill, 8th Marquess of Downshire (1929-2003)
• Arthur Francis Nicholas Wills Hill, 9th Marquess of Downshire (b. 1959)