According to a contemporary, Lord Burghley "confided in no one, had no close friends, nor did any other know his secrets". He was an intellectual though not contemplative as he was a man of action; and his actions were based on two aims: to exercise power in the affairs of England and to found a dynasty. He succeeded in both. 
He was clever and hardworking and became a page at court as well as studying at Grantham Grammar School, then later at St.John's College, Cambridge. The only mistake he seemed to have made was his 
first marriage to Mary Cheke. Her mother kept an ale-house and there was no dowry. Although William's father objected, they married in 1541. However, the marriage did not last long as she died two years later, leaving him with an infant son. 
In 1545 he married Mildred Cooke, daughter of Sir Anthony Cooke, governor of Prince Edward. She was one of the most learned women in England. He then became a Member of Parliament and attracted the attention of King Henry VIII. 
However, the reigns of King Edward VI and Queen Mary I were a testing period not only for the future Elizabeth I but also for William Cecil. Both had to manoeuvre between ruthless nobles and religious fanatics. With the army of the Duke of Somerset he went to Scotland and was almost killed at Pinkie. Returned to England, he became Somerset's personal secretary; and when Somerset was imprisoned, William Cecil followed him into the Tower. Soon he was released and two years later was knighted. After Somerset's execution Sir William worked for his successor, the Duke of Northumberland. However, in 1553 Northumberland demanded that his servants sign their approval to his changing the royal succession to Lady Jane Grey, Northumberland's daughter-in-law. At first Sir William refused and signed only after being ordered to do so by the boy-king, Edward VI. After this he wrote to Princess Mary to explain his actions and asked her forgiveness. 
When Mary became queen as a Protestant he resigned his offices and retired to the country. He invested in foreign trade as well as building a house at Burghley and another in London. He still performed tasks for the government but also kept in touch secretly with Princess Elizabeth. 
As soon as Elizabeth became Queen she appointed him as her chief minister. For many years England's policies were shaped by Queen Elizabeth and her trusted advisor who became known by his title of 
Lord Burghley. They were both realists willing to change policies when needed, often not taking any action but waiting for their opponents to make the first move which was often their error. 
William Cecil made England solvent again by restoring the nation's finances, reducing its debt and reinstituting the coinage. To restore religious peace the old order of priests and bishops was retained 
although breaking with the Pope and the Latin Mass. To restore peace with France, William Cecil and Elizabeth were willing to give up England's claims to Calais. In return the French withdrew their soldiers from Scotland which also restored peace with Scotland. According to William Cecil, "a reign gaineth more by one year's peace than ten years' war". Even though he preferred peace he made sure the army and navy were prepared as well as organising a powerful secret service. 
He served Queen Elizabeth I for forty years; yet this was not always easy as the Queen also had other favourites who resented him, his main opponent being Robert Dudley, Earl of Leicester. One of the 
greatest conflicts between Sir William Cecil and Elizabeth was the fate of Mary, Queen of Scots. Cecil wanted her executed but Elizabeth considered that executing a crowned queen a bad precedent. When at last Elizabeth did agree to sign Mary's death warrant, Cecil was banished from her presence for four months. 
In 1571 Elizabeth created him Baron Burghley and, a year later, Knight of the Garter and Lord Treasurer. A later offer of an earldom he refused on the grounds that it would involve him in too much 
expense. When at home his family and all his servants would dine together. However, no actors nor musicians were employed for entertainment while these lengthy meals took place as he preferred 
conversation; yet however high the level of conversation might be, politics were barred. He preferred science, history, antiquities and theology. 
He collected books, portraits, coins, busts from Rome and statues from Venice. His house became famous for both his library and garden. Despite taking great care with the education of his children, he was to be disappointed with the scholarly achievements of his eldest son. Fortunately his second son more than made up for this. 
By his second wife he had three children: Anne, Elizabeth and Robert. He loved them dearly but both daughters would be the cause of sorrow. Elizabeth married Lord Wentworth but died only two years 
later. In 1571, when Anne was only sixteen, Edward de Vere, Earl of Oxford, asked for her hand. Wealthy, handsome, a poet as well as a favourite of the Queen, he seemed a good husband for his "Tannakin". 
Although both Lord and Lady Burghley had their reservations, the marriage took place in December 1571. However, Burghley's fears were soon realised. Leaving his wife behind, the Earl of Oxford went to Italy from where, by 1575, Burghley received the news that the Earl was "a drunkard, a homosexual and an atheist". Later the Earl was also reputed to be William Shakespeare. Heart-broken, Anne died aged thirty-three. 
Burghley felt responsible for the Earl of Oxford's behaviour as he had educated him together with the sons of other aristocrats. By providing this education he had hoped to build up a class trained to 
devote themselves to the queen's service. 
By the time of the threat of the Spanish Armada in 1588, the country's administration was firmly established. Then in 1589 his wife died and, as she had been his only confidant, he said, "I am as lonely 
as an owl". From then onwards he dined alone in his chamber and did a great deal of his work in bed. 

In the last ten years of his life he trained his second son to be his successor. However, just as Burghley had been opposed by Leicester, in turn his son was now opposed by the Earl of Essex. In 1596 Robert Cecil was appointed the Queen's secretary and, when Burghley died in 1598, was replaced by him.
 

Source: Leo van de Pas