William Cecil was born in Bourn, Lincolnshire, in 1520. Educated at St. John's College, Cambridge, in 1541 he married Mary Cheke, the daughter of one of his university tutors. After her death he married Mildred Cooke in in 1545.
Cecil worked as a lawyer until 1542 when he entered the service of Edward Seymour, Duke of Somerset. When his patron fell from power Cecil was imprisoned. He was eventually released and in 1550 he served under John Dudley as Secretary of State.
Edward was suffering from tuberculosis and as his health deteriorated, John Dudley, persuaded the king to alter the succession in favour of his own daughter-in-law, Lady Jane Grey. She was declared queen three days after Edward's death. However, she was forced to abdicate nine days later in favour of Edward's half-sister, Mary Tudor. Cecil played a minor role in this conspiracy but powerful friends helped to protect him.
In 1558 Elizabeth appointed him as Chief Secretary of State. For the next forty years Cecil was the main architect of Elizabeth's religious and political policies. He also encouraged the creation of an intelligence-gathering service directed by Francis Walsingham.
In 1571 Cecil was created Baron Burghley. The following year he was appointed as Lord High Treasurer. In this post Cecil came into conflict with Robert Dudley. Cecil was strongly opposed to Dudley plans to lead military campaigns in favour of Protestantism in Europe.
In 1587 Cecil managed to persuade Elizabeth to order the execution of Mary Stuart. Afterwards Elizabeth regretted this decision and Cecil was temporarily banished from court. His son, Robert Cecil, became a Privy Councillor in 1591 and later served as Elizabeth's Secretary of State.
William Cecil died in 1598.