Parr took part in suppressing the rising in the north of England in 1537, and after serving as Member of Parliament for Northamptonshire was made Baron Parr in 1539.
In December 1543, just after his sister had married the king, he was created Earl of Essex, a title formerly held by his father-in-law, Henry Bourchier, who had died in March 1540.

He was Edward VI's "beloved uncle" and one of the most important men at Edward's court, especially during the time of John Dudley, 1st Duke of Northumberland's time as leader of the government.
Parr was lord-lieutenant in 1549 of five of the eastern counties (Cambridgeshire, Huntingdonshire, Bedfordshire, Northamptonshire and Norfolk), of Surrey in 1551, of Berkshire and Oxfordshire in 1552 and of Hertfordshire and Buckinghamshire in 1553.
He was appointed Lord Great Chamberlain from 1550 to 1553.
In this role, he welcomed Mary of Guise, Regent of Scotland, to Hampton Court Palace on behalf of the King in 1551.

Parr, and especially his wife, were leaders in the attempt to put Lady Jane Grey on the throne after Edward's death.
He was convicted of high treason, attainted, and sentenced to death on 18 August 1553 after the accession of Mary I. He was, however, released in the autumn.
His titles were restored to him by Elizabeth I in 1559.
Parr took part in suppressing the rising in the north of England in 1537, and after serving as Member of Parliament for Northamptonshire was made Baron Parr in 1539. In December 1543, just after his sister had married the king, he was created Earl of Essex, a title formerly held by his father-in-law, Henry Bourchier, who had died in March 1540.
He was Edward VI's "beloved uncle" and one of the most important men at Edward's court, especially during the time of John Dudley, 1st Duke of Northumberland's time as leader of the government. Parr was lord-lieutenant in 1549 of five of the eastern counties (Cambridgeshire, Huntingdonshire, Bedfordshire, Northamptonshire and Norfolk), of Surrey in 1551, of Berkshire and Oxfordshire in 1552 and of Hertfordshire and Buckinghamshire in 1553. He was appointed Lord Great Chamberlain from 1550 to 1553. In this role, he welcomed Mary of Guise, Regent of Scotland, to Hampton Court Palace on behalf of the King in 1551. 
Parr, and especially his wife, were leaders in the attempt to put Lady Jane Grey on the throne after Edward's death. He was convicted of high treason, attainted, and sentenced to death on 18 August 1553 after the accession of Mary I. He was, however, released in the autumn. His titles were restored to him by Elizabeth I in 1559.
William Parr, 1st Marquess of Northampton