Sir Daniel O'Brien, 1st Viscount Clare also called Donal (c. 1577 – 1666) was an Irish politician and soldier.

He joined Charles II of England in exile and was in his eighties made a viscount at the Restoration.

His parents were from different branches of the O'Briens, an important Gaelic Irish dynasty that descended from Brian Boru, medieval high king of Ireland.

In February 1599 O'Brien was attacked in his castle of Ibrickane, wounded, and taken prisoner by O'Donnell.

[23] At the election of the speaker O'Brien supported the Catholic candidate John Everard.

In the Irish Parliament of 1634–1635 he replaced his nephew Barnabas O'Brien, the future 6th Earl of Thomond, who had absented himself to England.

In June 1652, at Ross Castle near Killarney, O'Brien together with Lord Muskerry surrendered to Ludlow.