Sidney was born at Castle Barnard, the son of Robert Sidney, 1st Earl of Leicester, and his first wife, Barbara Gamage. Sidney served in the army in the Netherlands during his father"s governorship of Flushing, and was given command of an English regiment in the Dutch service in 1616.
He was educated at Christ Church, Oxford.
In 1610 he was created Knight of the Bath when Prince Henry was created Prince of Wales. He was elected Member of Parliament for Kent in 1621. In 1624 he was elected Member of Parliament for Monmouthshire.
He was re-elected Member of Parliament for Monmouthshire in 1625.
In 1626, he succeeded his father as Earl of Leicester in 1626. In 1631, he began the construction of Leicester House, a huge mansion on the site of what is now Leicester Square in London.
He was employed on diplomatic business in Denmark in 1632 and undertook further diplomatic work in France from 1636 to 1641. Lord Leicester was then appointed Lord Lieutenant of Ireland in place of The Earl of Strafford.
When the governorship of Dublin became vacant, Leicester appointed George Monck.
Charles I, however, overruled the appointment in favour of Lord Lambart. In 1643 he resigned without having set foot in Ireland. Lord Leicester died at Penshurst at the age of nearly 81.
He was "esteemed of great learning, observation and veracity".
Sidney married Dorothy Percy, the daughter of Henry Percy, 9th Earl of Northumberland. They had twelve children, including:
Dorothy (1617–1683), married Henry Spencer, 1st Earl of Sunderland (died 1643) then Robert Smith or Smythe.
Philip (1619–1697), the 3rd Earl, married Lady Catherine Cecil, daughter of William Cecil, 2nd Earl of Salisbury. Henry Sidney, 1st Earl of Romney (1641-1704), died unmarried and without issue.
Algernon (1622/3-1683) executed for his share in the Rye House Plot, died unmarried and without issue.
Robert, died young. Lucy (d 1685), married Sir John Pelham, 3rd Baronet. Philip and Algernon supported the Parliamentary cause in the English Civil War.
Useless Parliament; Happy Parliament. Addled Parliament]
He was elected Member of Parliament for Wilton in 1614. In 1618 he became a member of Gray"s Inn.
