Viscount Brouncker, of Lyons in the Province of Leinster, was a title in the Peerage of Ireland. It was created on 12 September 1645 for the courtier Sir William Brouncker. He was made Baron Brouncker, of Newcastle in the Province of Munster, at the same time, also in the Peerage of Ireland. He was succeeded by his eldest son, the second Viscount. He was a distinguished mathematician and also held political office. He was unmarried and was succeeded by his younger brother, the third Viscount. He served as Cofferer of the Household between 1680 and 1685. He was childless and the titles became extinct on his death in 1688.
Sir Henry Brouncker (d. 1607), father of the first Viscount, was Lord President of Munster.
Viscounts Brouncker (1645)
- William Brouncker, 1st Viscount Brouncker (1585–1645)
- William Brouncker, 2nd Viscount Brouncker (1620–1684)
- Henry Brouncker, 3rd Viscount Brouncker (1626–1688)