He was born in Althorp, Northamptonshire, the son of John Spencer and Mary, daughter of Sir Robert Catlyn.

Spencer held the office of Member of Parliament for Brackley from 1597 to 1598.

Anne of Denmark and Prince Henry came to Althorp on Sunday 25 June 1603 from Dingley.

Spencer welcomed them with a performance The Entertainment at Althorp, written by Ben Jonson.

On 5 August 1607 he was nominated with Sir Ralph Winwood joint representative of England at The Hague in the negotiations for peace between Spain and the United Netherlands.