Maynard was the son of John Maynard, who had been Member of Parliament for Street Albans in the first Parliament of Mary I of England in 1553-1554 (being one of the 39 members who absented themselves, rather than acknowledge the authority of the Pope), and his second wife, Dorothy, daughter of Robert Perrot.
He was secretary to Lord Burghley, the Lord High Treasurer, and by virtue of his position he was able to take advantage of troubled assets and gradually became a major landowner, especially in Essex. He served as Member of Parliament for Saint Albans in the parliaments of 1586, 1588, 1592 and 1597. "He sat on committees concerning recusancy, horse and cattle stealing, privileges, penal laws, painters and stainers, and fustians".
He was also summoned to the parliament of 1601 as a knight of the shire for Essex.
He was High Sheriff of Essex in the last year of Elizabeth’s reign (1603) and was knighted by her. In July 1603, following the accession of James I, he was appointed as Deputy Lieutenant for Essex (the new Lord Lieutenant being the Earl of Sussex).
He also developed a reputation as a moneylender. In 1595-1596, he acquired the manor of Tooting Graveney from James Harrington.
When the Queen visited in 1600, she was probably his guest.
The eldest, William, became the first Lord Maynard. Another, John, became a Knight of the Bath. He made his will on 20 August 1609 and it was proved on 18 May 1610.
He was buried at Little Easton, Essex, near Easton Lodge, a property granted to him by Queen Elizabeth in 1590.
